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One of the largest earthquakes in the Zagros region occurred on November 12, 2017, in Sarpol-e Zahab with Mw=7.3. We considered the aftershocks of this event and collected the S-wave amplitude spectra from 87 strong-motion records to determine the source, path, and site effects using a non-parametric generalized inversion technique. The grid-searching method based on Brune's X2 model was employed to determine some of the source parameters. The corner frequency and seismic moment vary from 1.11 to 5.14 Hz and from 9.12×1014 to 1.36×1017 N.m, respectively. Also, The seismic moment and the cube of corner frequency are inversely related to each other. The stress drop of earthquakes is determined with the e indicator. In this study e is equal to 1.91; thus this value indicates that frictional overshoot has occurred with the dynamic frictional stress larger than the final stress. The S-wave quality factor is estimated as Q=101f0.67. The value of Q0 is small, which is characteristic of an active tectonic environment. We compared the site effects that were calculated by GIT and H/V methods. In most cases, a very good agreement was observed and the small difference between them is mainly due to the constraints and assumptions of these methods. [ABSTRACT FROM AUTHOR]

Mapping variations in the attenuation of seismic energy is important for understanding dissipative mechanisms in the lithosphere, and for modeling ground shaking associated with earthquakes. We cross-correlate ambient seismic signal recorded across the EarthScope Transportable Array in the 3–15 s period range. We apply to the resulting cross correlations a new method to estimate lateral variations in Rayleigh-wave attenuation, as a function of period, beneath North America. Between 3 and 6 s, our maps are dominated by a strong eastward decrease in attenuation. This pattern vanishes at longer periods, confirming early observations based on regional earthquakes. Attenuation maps and phase-velocity maps are anti-correlated at periods between 3 and 6 s, but the anti-correlation is also largely lost at longer periods. This corresponds to the attenuation coefficient decreasing with period more rapidly in the west than in the east, while the change in phase velocity with period is more uniform across the continent. Our results point to a transition in the properties of upper-crustal materials with depth, probably related to the closure of fluid-filled cracks and pores, and imply that measures of attenuation from seismic noise carry significant information on crustal rheology. [ABSTRACT FROM AUTHOR]

We image seismic attenuation near the Hikurangi trench offshore New Zealand, using ocean bottom and land‐based seismometers, revealing high attenuation above a recurring shallow slow‐slip event and within the subducting Hikurangi Plateau. The Hikurangi subduction margin east of the North Island, New Zealand is the site of frequent shallow slow slip events. Overpressured fluids are hypothesized to lead to slow slip at shallow depths close to the oceanic trench. Seismic attenuation, energy loss of seismic waves, can be used to detect high temperatures, melt, the presence of fluids, and fractures. We use local earthquake P‐ and S‐waves from 180 earthquakes to invert for t*, and subsequently invert for Qp and Qs, offshore the North Island directly above the area of slow slip. We image Qp and Qs to ∼25 km depth, increasing resolution of previously identified coastal low Q (100–300), and finding a new region of even higher attenuation (Qp and Qs < 50–100) directly above the shallow slow slip event of 2014–2015, beneath the offshore seismic array. This highest attenuation is downdip of a subducting seamount, and is spatially correlated with a high seismic reflectivity zone and Vp/Vs > 1.85, all of which provide evidence for the presence of fluids. The Qp and Qs is low at the trench (<50–100) and in the subducting plate (100–200), suggesting that seismic wave scattering due to faults, fractures, and the inherent heterogeneous composition of the Hikurangi Plateau, a large igneous province, plays a role in seismic attenuation. Plain Language Summary: The Hikurangi Margin is a major subduction zone which has produced earthquakes that lead to tsunamis, which could endanger people living on the North Island of New Zealand and the fishing and shipping industry. Mysterious slow earthquakes, or slow slip events, happen near the shore where large earthquakes have happened in the past. Scientists do not yet understand why these events occur, but it may be because of fluids on the plate that is subducting beneath the North Island. These fluids can come from chemical reactions or the water content of the sediment on the incoming plate. Our study finds evidence of fluids in the area of the plate interface by measuring energy loss from earthquakes offshore of the North Island, which we use to create a 3D image of where energy is lost. As seismic waves travel through rock, they lose a lot of energy when they encounter fluids, like water, and as they pass through layered, volcanic rocks. We combine our study with other studies to show where pockets of fluids are likely located near the subducting plate, which will help scientists in future field studies and also help us understand why slow slip events occur at the Hikurangi Margin. Key Points: Low Qp and Qs (<50–100) coincides with high Vp/Vs and are interpreted as fluid near the plate interface, downdip of a subducted seamountLow Qp (100–200) in the Hikurangi Plateau large igneous province suggests a thicker (~23 km) oceanic crustNear‐trench low Qp and Qs (<50–100) may indicate seismic wave scattering from faults in the Hikurangi Basement and the deformed upper plate [ABSTRACT FROM AUTHOR]

Investigating heterogeneous structures beneath active volcanoes is important for better understanding of volcanic activity and improved mitigation of volcanic risk. In central Japan, Hakone volcano has recently shown shallow earthquake swarms and deep low‐frequency earthquakes (DLFEs), which are probably related to geothermal or deep magmatic activity. In order to image the feeding system beneath this volcano, we estimate 3‐D P wave attenuation structure using waveform data recorded at permanent and densely distributed temporary seismograph stations. We first determine corner frequencies of the earthquakes and then perform a joint inversion to obtain attenuation terms (t*) and site responses. Values of t* are finally inverted to estimate the attenuation structure to a depth of 50 km. High‐attenuation zones at depths ≤5 km suggest that fracture zones are permeated with hydrothermal fluids. A high–strain rate zone revealed by geodetic observations is spatially correlated with a high‐attenuation volume at depths of 5–10 km, suggesting that the anelastic deformation is dominant in the high‐attenuation zones. A subvertical volume of moderate attenuation that is imaged at depths of 10–20 km beneath Hakone volcano is connected to the top of a zone of partial melting beneath Mt. Fuji at depths ≥30 km through a subhorizontal channel at a depth of ~25 km. DLFEs in the lower crust and fluid‐related activity such as earthquake swarms in the upper crust occur in this volume. The zone is thus interpreted as a fluid‐bearing pathway, which allows the rise of magmatic fluids to Hakone volcano. Key Points: Large historical earthquakes occurred at the edge of high‐attenuation anomaliesA deep magmatic system to Mt. Fuji and Hakone volcano is common but is separated at a depth of ~25 kmMagma chamber with the dimension of as large as ~10 km is unlikely to exist at depths of 10–20 km beneath Hakone volcano [ABSTRACT FROM AUTHOR]

Observed ground-motion intensity for six earthquakes of Mw = 6.0–6.2 that occurred in China's North–South Seismic Zone (NSSZ) was compared with predicted medians from the BSSA14 model. The resulting between-event (δBe) and within-event (δWes) residuals for peak ground acceleration and pseudo-spectral acceleration up to 5.0 s were used to investigate the impact of source effects and path propagation on the regional variability in observed ground-motion amplitude within the NSSZ. Although the magnitude and fault type were similar among the six earthquakes, the results showed that their source effects were significantly different, which contributed in part to the regional variability in observed ground-motion amplitude. Estimated values for stress drop were found to mirror the trend in variation of the δBe values for short-period ground motions in the six earthquakes. This suggests that stress drop is an important factor for accurate representation of source effects and should be considered in the functional form of ground-motion prediction equations. Anelastic attenuation of ground motion was found to be considerably different in local areas of the NSSZ, which may constitute the primary reason for the regional variability in the observed ground-motion amplitude. The variation in δWes values confirmed that regional adjustment of anelastic attenuation in the BSSA14 model is applicable to some local areas (i.e., around the Longmenshan fault) but not to the NSSZ in its entirety. [ABSTRACT FROM AUTHOR]

S -wave spectral amplitudes from 312 crustal earthquakes recorded at the Iranian National Broadband Seismic Network in the Alborz region between 2005 and 2017 are analysed in order to evaluate earthquake source parameters, path attenuation and site amplification functions using the non-parametric generalized inversion technique (GIT). We exploit a total number of 1117 seismograms with M L 3–5.6 in the frequency range 0.3–20 Hz. The evaluated non-parametric attenuation functions decay uniformly with distance for the entire frequency range and the estimated S -wave quality factor shows low Q values with relatively strong frequency dependence. We assume the omega-square source model to retrieve earthquake source parameters from the inverted source spectra. The obtained stress drops range from 0.02 to 16 MPa with a mean value of 1.1 MPa. Stress drop and radiated energy show fairly self-similar scaling with seismic moment over the available magnitude range; however, the magnitude range of this study is too narrow to draw a definite conclusion on source scaling characteristics. The obtained moment magnitude M w and the local magnitude M L are linearly correlated and approximately equivalent in the range of M w 3–4. For larger events, M w generally underestimates M L by about 0.1–0.5 magnitude units. The estimated site amplification functions for horizontal component (GIT H) are nearly flat with no obvious pre-dominant frequency peaks for most stations, as expected for the sites of permanent broad-band seismic stations located on rock, though a few stations show amplification peaks from 1 to 8 Hz, with a maximum amplification of about a factor of 7 with respect to the reference site. The evaluated site responses for the vertical components present remarkable amplification or deamplification, leading to differences of the H/V amplitude levels in comparison with the GIT H amplification curves. The results of this study provide a valuable basis for predicting appropriate ground motions in a context of seismic hazard assessment. [ABSTRACT FROM AUTHOR]

The crack density within a fault's damage zone is thought to vary as seismic rupture is approached, as well as in the postseismic period. Moreover, external stress loads, seasonal or tidal, may also change the crack density in rocks, and all such processes can leave detectable signatures on seismic attenuation. Here we show that attenuation time histories from the San Andreas Fault at Parkfield are affected by seasonal loading cycles, as well as by 1.5–3‐year periodic variations of creep rates, consistent with Turner et al. (2015, https://doi.org/10.1002/2015JB011998), who documented a broad spectral peak, between 1.5 and 4 years, of the spectra calculated over the activity of repeating earthquakes, and over InSAR time series. After the Parkfield main shock, we see a clear modulation between seismic attenuation correlated to tidal forces. Opposite attenuation trends are seen on the two sides of the fault up to the M6.5 2003 San Simeon earthquake, when attenuation changed discontinuously, in the same directions of the relative trends. Attenuation increased steadily of over one year on the SW side of the San Andreas Fault, until the San Simeon earthquake, whereas it decreased steadily on the NE side of the San Andreas Fault, roughly for the six months prior to the event. Random fluctuations are observed up to the 2004 M6 Parkfield main shock, when rebounds in opposite directions are observed, in which attenuation decreased on the SW side, and increased on the NE side. Key Points: Seismic attenuation fluctuates with periods related to solid tides and seasonal loading, indicating strong sensitivity to stress changesAttenuation on the opposite sides of the San Andreas Fault shows mirror‐like anomalies before and after the 2004 Parkfield main shockEarthquake‐induced damage increases the sensitivity of seismic attenuation to periodic stress fluctuations [ABSTRACT FROM AUTHOR]

Highlights • A tomographic image of Pg Q is developed for Nepal Himalaya. • Intrinsic attenuation plays a major role in causing the high attenuation. • Low Q structure associated with the LVL may imply a weak crust, favorable zone for future rupture. Abstract We investigate the spatial variations of Pg attenuation structure in Nepal Himalaya. We implement the "Two-Station method" on 2325 waveforms obtained from 435 events recorded at 151 stations deployed across Nepal Himalaya to measure the Pg -wave quality factor (Q). These station-station measurements are inverted further for investigating the spatial variations of Pg attenuation using a back projection algorithm. The model contains variations across the region, with much of the region being dominated by high attenuation. It is observed that the areas around the existing faults and lineaments exhibit very low Q values. A few exceptional high Q pockets are observed to be limited predominantly in the north western side of our study area. We hypothesize that intrinsic attenuation plays a major role in causing the high apparent Pg attenuation in the crust of Nepal Himalaya. This may be mainly caused by highly pressurized fluids trapped within a thin low velocity layer (LVL) at shallow depths. Moreover it is interesting to observe that all the past earthquakes of M w > 7 since 1934, fall into the regions of low Q values but not the lowest. It may be anticipated that the very low Q areas are too weak to sustain the accumulation of high energy release during a large magnitude earthquake. Therefore the observed low Q structures across the study area may imply a weak crust and subsequently a favorable zone for future rupture. [ABSTRACT FROM AUTHOR]

We present a new 3-D anelastic attenuation model for the upper mantle of the southern Aegean Sea subduction area, by inverting whole-path attenuation operators (t*) data, for both P - and S - waves. For the attenuation tomography, we have employed 383 intermediate-depth earthquakes, recorded by two temporary networks between 2002 and 2007, namely the EGELADOS seismic monitoring project installed in the broader southern Aegean Sea area, and the smaller local CYCNET network which operated in the central part of southern Aegean Sea. Frequency-independent t * values were computed for both P and S waves from acceleration amplitude spectra using two approaches. Initially, we estimated t * values from the slope of the acceleration spectra above the corner frequency, using an automated procedure based on the signal-to-noise ratio. A more standard approach was also followed, where t* values were estimated from the manual (visual) selection of the linearly decaying segment of the acceleration spectrum by an analyst. The t* value data set was inverted to determine the 3-D Q -structure of Southern Aegean Sea, similar to traveltime tomography. The inversion results show high P - and S -wave attenuation in the upper mantle of the back-arc area, with significant low QP and QS anomalies in the mantle wedge of the subducting eastern Mediterranean slab under the Aegean, and higher QP and QS values in the outer Hellenic arc. The strongest anomalies are observed beneath and to the north of the volcanic arc, mainly at depths between 60 and 80 km. At larger depths, the lowest QP and QS anomalies are observed in the area of highest deep (100–170 km) microseismicity, in the easternmost part of the Hellenic volcanic arc. P -wave attenuation models from both the automated and manual t* determination approach are in good agreement. On the contrary, the automated S -wave attenuation models show significant but random spatial variability, while the manual S -wave attenuation models show a similar spatial pattern with the P -wave results, with stronger attenuation in the mantle wedge area. The final anelastic attenuation models are in good agreement with previous results for the study area (e.g. 3-D velocity models, Ground Motion Prediction Equations proposed for intermediate-depth events), as well as with attenuation models proposed for similar subduction zones. [ABSTRACT FROM AUTHOR]

Many observations of seismic waves from local earthquakes are interpreted in terms of the frequency-dependent quality factor Qf=Q0fη, where η is often close to or exceeds one. However, such steep positive frequency dependencies of Q require careful analysis with regard to their physical consistency. In particular, the case of η = 1 corresponds to frequency-independent (elastic) amplitude decays with time and consequently requires no Q-type attenuation mechanisms. For η > 1, several problems with physical meanings of such Q-factors occur. First, contrary to the key premise of seismic attenuation, high-frequency parts of the wavefield are enhanced with increasing propagation times relative to the low-frequency ones. Second, such attenuation cannot be implemented by mechanical models of wave-propagating media. Third, with η > 1, the velocity dispersion associated with such Q(f) occurs over unrealistically short frequency range and has an unexpected oscillatory shape. Cases  η = 1 and  η > 1 are usually attributed to scattering; however, this scattering must exhibit fortuitous tuning into the observation frequency band, which appears unlikely. The reason for the above problems is that the inferred Q values are affected by the conventional single-station measurement procedure. Both parameters Q0 and are apparent, i.e., dependent on the selected parameterization and inversion method, and they should not be directly attributed to the subsurface. For η  ≈ 1, parameter Q0 actually describes the frequency-independent amplitude decay in access of some assumed geometric spreading t−α, where α is usually taken equal one. The case η > 1 is not allowed physically and could serve as an indicator of problematic interpretations. Although the case 0<η<1 is possible, its parameters Q0 and may also be biased by the measurement procedure. To avoid such difficulties of Q-based approaches, we recommend measuring and interpreting the amplitude-decay rates (such as parameter α) directly. [ABSTRACT FROM AUTHOR]

We estimated the radiated seismic energy (E S) of 65 earthquakes located in the south–central region of the Gulf of California. Most of these events occurred along active transform faults that define the Pacific–North America plate boundary and have magnitudes between M 3.3 and M 5.9. We corrected the spectral records for attenuation using non-parametric S -wave attenuation functions determined with the whole data set. The path effects were isolated from the seismic source using a spectral inversion. We computed radiated seismic energy of the earthquakes by integrating the square velocity source spectrum and estimated their apparent stresses. We found that most events have apparent stress between 3 × 10−4 and 3 MPa. Model independent estimates of the ratio between seismic energy and moment (E S/ M 0) indicate that this ratio is independent of earthquake size. We conclude that in general the apparent stress is low (σa  < 3 MPa) in the south–central and southern Gulf of California. [ABSTRACT FROM AUTHOR]

Comprised of S waves trapped in the Earth's crust, the high-frequency (2–10 Hz) Lg wave is important to discriminating earthquakes from explosions by comparing its amplitude and waveform to those of Pg and Pn waves. Lateral variations in crustal structure, including variations in crustal thickness, intrinsic attenuation and scattering, affect the efficiency of Lg propagation and its consistency as a source discriminant at regional (200–1500 km) distances. To investigate the effects of laterally varying Earth structure on the efficiency of propagation of Lg and Pg, we apply a radiative transport algorithm to model complete, high-frequency (2–4 Hz), regional coda envelopes. The algorithm propagates packets of energy with ray theory through large-scale 3-D structure and includes stochastic effects of multiple scattering by small-scale heterogeneities within the large-scale structure. Source-radiation patterns are described by moment tensors. Seismograms of explosion and earthquake sources are synthesized in canonical models to predict effects on waveforms of paths crossing regions of crustal thinning (pull-apart basins and ocean/continent transitions) and thickening (collisional mountain belts). For paths crossing crustal thinning regions, Lg is amplified at receivers within the thinned region but strongly disrupted and attenuated at receivers beyond the thinned region. For paths crossing regions of crustal thickening, Lg amplitude is attenuated at receivers within the thickened region, but experiences little or no reduction in amplitude at receivers beyond the thickened region. The length of the Lg propagation within a thickened region and the complexity of over- and underthrust crustal layers can produce localized zones of Lg amplification or attenuation. Regions of intense scattering within laterally homogeneous models of the crust increase Lg attenuation but do not disrupt its coda shape. [ABSTRACT FROM AUTHOR]

Abstract Attenuation of seismic wave energy of Delhi and its surrounding regions has been estimated using coda of local earthquakes. Estimated quality factor (Q c) values are strongly dependent on frequency and lapse time. Frequency dependence of Q c has been estimated from the relationship Q c (f) = Q 0 f n for different lapse time window lengths. Q 0 and n values vary from 73 to 453 and 0.97 to 0.63 for lapse time window lengths of 15 s to 90 s respectively. Average estimated frequency dependent relation is, Q c (f) = 135 ± 8 f 0.96±0.02 for the entire region for a window length of 30 s, where the average Q c value varies from 200 at 1.5 Hz to 1962 at 16 Hz. These values show that the region is seismically active and highly heterogeneous. The entire study region is divided into two sub-regions according to the geology of the area to investigate if there is a spatial variation in attenuation characteristics in this region. It is observed that at smaller lapse time both regions have similar Q c values. However, at larger lapse times the rate of increase of Q c with frequency is larger for Region 2 compared to Region 1. This is understandable, as it is closer to the tectonically more active Himalayan ranges and seismically more active compared to Region 1. The difference in variation of Q c with frequencies for the two regions is such that at larger lapse time and higher frequencies Region 2 shows higher Q c compared to Region 1. For lower frequencies the opposite situation is true. This indicates that there is a systematic variation in attenuation characteristics from the south (Region 1) to the north (Region 2) in the deeper part of the study area. This variation can be explained in terms of an increase in heat flow and a decrease in the age of the rocks from south to north. Highlights • Coda Q of Delhi and its surrounding regions has been estimated using Q c (f) = Q 0 f n relationship. • Estimated Q c values are strongly dependent on the frequency and lapse time. • The frequency dependent relationship is estimated as Q c (f) = 135 ± 8 f 0.96±0.02 for 30 s window length. • The Q0 and n values show that the medium is highly heterogeneous. • Obtained estimates are compatible to other tectonically active regions of the world. [ABSTRACT FROM AUTHOR]

Alluvial valleys generate strong effects on earthquake ground motion (EGM). These effects are rarely accounted for even in site-specific studies because of (a) the cost of the required geophysical surveys to constrain the site model, (b) lack of data for empirical prediction, and (c) poor knowledge of the key controlling parameters. We performed 3D, 2D and 1D simulations for six typical sedimentary valleys of various width and depth, and for a variety of modifications of these 6 “nominal models” to investigate sensitivity of EGM characteristics to impedance contrast, attenuation, velocity gradient and geometry. We calculated amplification factors, and 2D/1D and 3D/2D aggravation factors for 10 EGM characteristics, using a representative set of recorded accelerograms to account for input motion variability. The largest values of the amplification and aggravation factors are found for the Arias intensity and cumulative absolute velocity, the lowest for the root-mean-square acceleration. The aggravation factors are largest for the vertical component. For each model, at least one EGM characteristic exhibits a significant 2D/1D aggravation factor, while all EGM characteristics exhibit significant 2D/1D aggravation factor on the vertical component. For all investigated sites, there is always an area in the valley for which 1D estimates are not sufficient. 2D estimates are insufficient at several sites. The key structural parameters are the shape ratio and overall geometry of the sediment-bedrock interface, impedance contrast at the sediment-bedrock interface, and attenuation in sediments. The amplification factors may largely exceed the values that are usually considered in GMPEs between soft soils and rock sites. [ABSTRACT FROM AUTHOR]

We perform a systematic comparison between local and moment magnitudes in Greece for the period 2008-2016 when both magnitudes have been determined using waveform data recorded by the Hellenic Unified Seismic Network (HUSN). Differences between the two magnitudes scales on average do not exceed ± 0.2 units as has been found in other regions worldwide. A recalculation of local magnitude using magnitude residuals for each HUSN station shows that station site conditions have very little influence on the difference between local and moment magnitude. It is therefore more likely that wave propagation effects and in rare cases, anomalous source properties are dominant factors in shaping this difference. General orthogonal regression is applied to the whole dataset and also to subsets covering different areas of Greece or different time period to calibrate the one magnitude scale against the other using a linear model. The resulting relationships differ very little, suggesting that there is no significant regional/temporal variation between local and moment magnitudes. While these relationships predict that local magnitude is very close to moment magnitude if both are determined using HUSN data, the comparison with Global CMT moment magnitude (with Mw in the range 4.5-6.2) shows that it is larger than local magnitude by 0.18 units. These results are particularly important for converting local magnitudes to equivalent moment magnitudes and thus homogenize the Greek earthquake catalog. [ABSTRACT FROM AUTHOR]

We have investigated several relationships between ML, M(NEIC) and Mw for the earthquakes locally recorded in the Saint Peter and Saint Paul Archipelago (SPSPA), Equatorial Atlantic. Because we only have one station in the area, we could not derive attenuation relations for events recorded at different distances at different stations. Our approach was then to compare our ML estimates with magnitudes reported by NEIC. This approach produced acceptable results particularly for epicentral distance smaller than 100 km. For distances greater that 100 km, there is a systematic increase in the residuals probable due to the lack of station correction and our inability to accurately estimate Q. We also investigate the Mw—M(NEIC) relationship. We find that Mw estimates using S-wave produce smaller residuals when compared with both M(NEIC). Finally, we also investigate the ML—Mw relationship and observe that given the data set we have, the 1:1 holds. We believe that the use of the present methodologies provide consistent magnitude estimates between all the magnitudes investigated that could be used to better assess seismic hazard in the region. [ABSTRACT FROM AUTHOR]

We studied the attenuation of coda waves and its frequency and lapse-time dependence in northern Morocco. We analysed coda waves of 66 earthquakes recorded in this region during 2008 for four lapse time windows of length 30, 40, 50, and 60 s, and at five frequency bands with central frequency in the range of 0.75-12 Hz. We determined the frequency dependent Qc relation for the horizontal (NS and EW) and vertical (Z) component seismograms. We analyzed three-component broadband seismograms of 66 local earthquakes for determining coda-Q based on the single back-scattering model. The Qc values show strong frequency dependence in 1.5-12 Hz that is related to high degree of heterogeneity of the medium. The lapse time dependence of Qc shows that Q0 (Qc at 1 Hz) significantly increases with lapse time that is related to the depth dependence of attenuation and hence of the level of heterogeneity of the medium. The average frequency-dependent Qc(f) values are Qc=(143.75±1.09)f(0.864±0.006),Qc=(149.12±1.08)f(0.85±0.005) and Qc=(140.42±1.81)f(0.902±0.004) for the vertical, north-south and east-west components of motion, respectively. The frequency-dependent Qc(f) relations are useful for evaluating source parameters (Singh et al. 2001), which are the key inputs for seismic hazard assessment of the region. [ABSTRACT FROM AUTHOR]

We extend to intermediate and deep earthquakes the slowness parameter Θ originally introduced by Newman and Okal (1998). Because of the increasing time lag with depth between the phases P, pP and sP , and of variations in anelastic attenuation parameters t ∗ , we define four depth bins featuring slightly different algorithms for the computation of Θ . We apply this methodology to a global dataset of 598 intermediate and deep earthquakes with moments greater than 10 25 dyn ∗ cm. We find a slight increase with depth in average values of Θ (from −4.81 between 80 and 135 km to −4.48 between 450 and 700 km), which however all have intersecting one- σ bands. With widths ranging from 0.26 to 0.31 logarithmic units, these are narrower than their counterpart for a reference dataset of 146 shallow earthquakes ( σ = 0.55 ). Similarly, we find no correlation between values of Θ and focal geometry. These results point to stress conditions within the seismogenic zones inside the Wadati-Benioff slabs more homogeneous than those prevailing at the shallow contacts between tectonic plates. [ABSTRACT FROM AUTHOR]

The properties of the source spectra of local shallow-focus earthquakes on Kamchatka in the range of magnitudes M = 3.5-6.5 are studied using 460 records of S-waves obtained at the PET station. The family of average source spectra is constructed; the spectra are used to study the relationship between M and the key quasi-dimensionless source parameters: stress drop Δσ and apparent stress σ. It is found that the parameter Δσ is almost stable, while σ grows steadily as the magnitude M increases, indicating that the similarity is violated. It is known that at sufficiently large M the similarity hypothesis is approximately valid: both parameters Δσ and σ do not show any noticeable magnitude dependence. It has been established that M ≈ 5.7 is the threshold value of the magnitude when the change in regimes described occurs for the conditions on Kamchatka. [ABSTRACT FROM AUTHOR]

Seismic attenuation modeling is a core element in earthquake disaster assessment and earthquake early warning. In this paper, a novel nonparametric methodology, namely Bayesian Nonparametric General Regression (BNGR), is introduced for the modeling of peak ground acceleration attenuation relationship. In contrast to most existing methods, this method does not require a prescribed functional form of the attenuation relationship. Furthermore, it selects the proper set of variables necessary to model this relationship. Moreover, the proposed model does not only consider the epicentral distance but also the location of the measured station so it allows for the modeling of the attenuation directivity. The proposed method is demonstrated with a case study using a comprehensive database of ground motion records at 271 monitoring stations for the 2008 Ms 8.0 Wenchuan earthquake. Results show that the proposed methodology is capable to represent the seismic attenuation relationship. Furthermore, the contour plots of the peak ground acceleration provides valuable information for the study of the earthquake directivity characteristics. [ABSTRACT FROM AUTHOR]

We present the frequency-dependent attenuation model for Fourier amplitude spectra of strong earthquake ground motion in Serbia from intermediate depth earthquakes in the Vrancea source zone in Romania. The development of this type of scaling is the essential first step toward developing the corresponding attenuation and scaling equations for pseudo relative velocity spectra (PSV), which are necessary for seismic macro- and microzoning in the territory of Serbia. Such scaling is necessary because the Vrancea source zone produces large earthquakes with shaking that attenuates differently from the local earthquakes in Serbia. Development of such a scaling model is associated with several difficulties, the principal one being the lack of recorded strong motion accelerograms at epicentral distances exceeding 300 km. To reduce uncertainties with such scaling, we require our preliminary scaling equations to be consistent with independent estimates of seismic moment, stress drop, and radiated wave energy. In the future, when the recorded strong motion data from Vrancea earthquakes increases several-fold of what it is today, it will become possible to perform this analysis again, thus leading to more reliable and permanent scaling estimates. [ABSTRACT FROM AUTHOR]

On 2013 April 13, an inland earthquake of Mw 5.8 occurred in Awaji Island, which forms the western boundary of the Osaka sedimentary basin in western Japan. The strong ground motion data were collected from more than 100 stations within the basin and it was found that in the Osaka Plain, the pseudo velocity response spectra at a period of around 6.5 s were significantly larger than at other stations of similar epicentral distance outside the basin. The ground motion lasted longer than 3 min in the Osaka Plain where its bedrock depth spatially varies from approximately 1 to 2 km. We modelled long-period (higher than 2 s) ground motions excited by this earthquake, using the finite difference method assuming a point source, to validate the present velocity structure model and to obtain better constraint of the attenuation factor of the sedimentary part of the basin. The effect of attenuation in the simulation was included in the form of Q(f) = Q0(f/f0), where Q0 at a reference frequency f0 was given by a function of the S-wave velocity, Q0 = αVS. We searched for appropriate Q0 values by changing α for a fixed value of f0 = 0.2 Hz. It was found that values of α from 0.2 to 0.5 fitted the observations reasonably well, but that the value of α = 0.3 performed best. Good agreement between the observed and simulated velocity waveforms was obtained for most stations within the Osaka Basin in terms of both amplitude and ground motion duration. However, underestimation of the pseudo velocity response spectra in the period range of 5-7 s was recognized in the central part of the Osaka Plain, which was caused by the inadequate modelling of later phases or wave packets in this period range observed approximately 2 min after the direct S-wave arrival.We analysed this observed later phase and concluded that it was a Love wave originating from the direction of the east coast of Awaji Island. [ABSTRACT FROM AUTHOR]

The problem of active vibration control for uncertain linear structural systems with control forces input timedelay is investigated in this study. First, the original structural equation is converted to a state-space model by utilizing the matrix transformation. Second, according to the obtained model and a special Lyapunov functional, a sufficient condition is achieved for the closed-loop system to be stable with a prescribed level of disturbance attenuation. Then, in terms of solving these linear matrix inequalities (LMIs), the state-feed controller is achieved to stabilize the structural system with the performance ∥ z∥ < γ∥ ω∥. Third, by introducing the rank-1 vector to describe the system uncertainties, the uncertain system description is obtained, and the stabilizing condition is extended to the uncertain case. Finally, examples are given to show the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Fuzzy logic techniques have been widely used in civil and earthquake engineering applications in the past four decades. However, no thorough research studies were conducted to use them for deriving attenuation relationships for peak ground accelerations (PGA). This paper is an attempt to fill this gap by employing a fuzzy approach with fuzzy sets for earthquake magnitude and distance from source with the objective of proposing new ground motion attenuation models. Recent earthquake records from USA and Taiwan with magnitudes 5 or greater were used; and consisted of horizontal peak ground acceleration recorded on three different site conditions: rock, soil and soft soil. The use of Fuzzy models to quantify ground motion records, which are typically characterized by a high level of uncertainty, leads to a rational analytical tool capable of predicting accurate results. Testing of the fuzzy model with an independent data set confirmed its accuracy in predicting PGA values. [ABSTRACT FROM AUTHOR]

The problem of finite-time vibration control of earthquake excited linear structures with input time-delay and saturation is concerned in this paper. The objective of designing controllers is to guarantee the finite-time stability of closed-loop systems while attenuating earthquake-induced vibration of the structures. First, based on matrix transformation, the structural system is described as a state-space model, which contains actuator saturation and input time-delay. Then, based on a Lyapunov functional and finite-time stability analysis method, some sufficient conditions for the existence of saturation-tolerant finite-time vibration-attenuation controllers are obtained. By solving these conditions, the desired controllers can be obtained for the closed-loop system to be finite-time stable with a prescribed level of disturbance attenuation. It is shown by the simulation results that compared with some Lyapunov asymptotic stability results, finite-time stability control can result in better state responses. Furthermore, saturation-tolerant controller can result in a much lower controller gain than the ones without considering actuator saturations. [ABSTRACT FROM AUTHOR]

This article presents comparisons among the five ground-motion models described in other articles within this special issue, in terms of data selection criteria, characteristics of the models and predicted peak ground and response spectral accelerations. Comparisons are also made with predictions from the Next Generation Attenuation (NGA) models to which the models presented here have similarities (e.g. a common master database has been used) but also differences (e.g. some models in this issue are nonparametric). As a result of the differing data selection criteria and derivation techniques the predicted median ground motions show considerable differences (up to a factor of two for certain scenarios), particularly for magnitudes and distances close to or beyond the range of the available observations. The predicted influence of style-of-faulting shows much variation among models whereas site amplification factors are more similar, with peak amplification at around 1s. These differences are greater than those among predictions from the NGA models. The models for aleatory variability (sigma), however, are similar and suggest that ground-motion variability from this region is slightly higher than that predicted by the NGA models, based primarily on data from California and Taiwan. [ABSTRACT FROM AUTHOR]

An actuator and sensor allocation approach is proposed for the design of coupled-adjacent-building vibration suppression under seismic excitation. This paper first establishes a full-order model of adjacent buildings with the location information of actuators and sensors. Then, the order of the model is reduced via modal cost analysis, by retaining the modes contributing the most. In view of the fact that the output powers of the actuators are limited, this paper brings forward a mixed H\infty/GH2 control. By considering that not all the states of the system can be measured by the sensors, a dynamic output feedback controller is designed. The genetic algorithm is employed to obtain the locations of the actuators and sensors, as well as the corresponding controller. With the proposed approach, the allocation problem is solved, and the vibration of coupled adjacent buildings is attenuated at a sufficiently low level with constrained acting forces. Simulations demonstrate the effectiveness and robustness of the proposed approach in attenuating building vibration under earthquake excitation. [ABSTRACT FROM PUBLISHER]

The characteristics of the attenuation field of short-period shear waves in the region of Nevada nuclear test site (NNTS) are studied. The seismograms of underground nuclear explosions (UNEs) and earthquakes recorded by three seismic stations in 1975-2012 at the epicentral distances of up to 1000 km are processed by the methods based on the analysis of the amplitude ratios of Sn to Pn and Lg to Pg waves, as well as the S-coda envelopes for close events. It is shown that the structure of the attenuation field in the Earth's crust and upper mantle in the NNTS region experienced significant temporal variations during the interval of nuclear operations. The strongest variations were associated with UNEs conducted in the Pahute Mesa area, which held about two-thirds of the most intense explosions. Our data indicate that temporal variations in the structure of the attenuation field are related to the migration of deep fluids. A comparison of the general characteristics of the attenuation field in the regions of the three large nuclear test sites is presented. [ABSTRACT FROM AUTHOR]

We present a new measure of earthquake clustering and explore its use for comparing the performance of three different declustering methods. The advantage of this new clustering measure over existing techniques is that it can be used for non-Poissonian background seismicity and, in particular, to compare the results of declustering algorithms where different background models are used. We use our approach to study inter-event times between successive earthquakes using earthquake catalog data from Japan and southern California. A measure of the extent of clustering is introduced by comparing the inter-event time distributions of the background seismicity to that of the whole observed seismicity. Theoretical aspects of the clustering measure are then discussed with respect to the Poissonian and Weibull models for the background inter-event time distribution. In the case of a Poissonian background, the obtained clustering measure shows a decrease followed by an increase, defining a V-shaped trend, which can be explained by the presence of short- and long-range correlation in the inter-event time series. Three previously proposed declustering methods (i.e., the methods of Gardner and Knopoff, Reasenberg, and Zhuang et al.) are used to obtain an approximation of the residual 'background' inter-event time distribution in order to apply our clustering measure to real seismicity. The clustering measure is then estimated for different values of magnitude cutoffs and time periods, taking into account the completeness of each catalog. Plots of the clustering measure are presented as clustering attenuation curves (CACs), showing how the correlation decreases when inter-event times increase. The CACs demonstrate strong clustering at short inter-event time ranges and weak clustering at long time ranges. When the algorithm of Gardner and Knopoff is used, the CACs show strong correlation with a weak background at the short inter-event time ranges. The fit of the CACs using the Poissonian background model is successful at short and intermediate inter-event time ranges, but deviates at long ranges. The observed deviation shows that the residual catalog obtained after declustering remains non-Poissonian at long time ranges. The apparent background fraction can be estimated directly from the CAC fit. The CACs using the algorithms of Reasenberg and Zhuang et al. show a relatively similar behavior, with a time correlation decreasing more rapidly than the CACs of Gardner and Knopoff for shorter time ranges. This study offers a novel approach for the study of different types of clustering produced as a result of various hypotheses used to account for different backgrounds. [ABSTRACT FROM AUTHOR]

This paper presents a new hazard-consistent ground motion characterization of the Itoiz dam site, located in Northern Spain. Firstly, we propose a methodology with different approximation levels to the expected ground motion at the dam site. Secondly, we apply this methodology taking into account the particular characteristics of the site and of the dam. Hazard calculations were performed following the Probabilistic Seismic Hazard Assessment method using a logic tree, which accounts for different seismic source zonings and different ground-motion attenuation relationships. The study was done in terms of peak ground acceleration and several spectral accelerations of periods coinciding with the fundamental vibration periods of the dam. In order to estimate these ground motions we consider two different dam conditions: when the dam is empty ( T = 0.1 s) and when it is filled with water to its maximum capacity ( T = 0.22 s). Additionally, seismic hazard analysis is done for two return periods: 975 years, related to the project earthquake, and 4,975 years, identified with an extreme event. Soil conditions were also taken into account at the site of the dam. Through the proposed methodology we deal with different forms of characterizing ground motion at the study site. In a first step, we obtain the uniform hazard response spectra for the two return periods. In a second step, a disaggregation analysis is done in order to obtain the controlling earthquakes that can affect the dam. Subsequently, we characterize the ground motion at the dam site in terms of specific response spectra for target motions defined by the expected values SA ( T) of T = 0.1 and 0.22 s for the return periods of 975 and 4,975 years, respectively. Finally, synthetic acceleration time histories for earthquake events matching the controlling parameters are generated using the discrete wave-number method and subsequently analyzed. Because of the short relative distances between the controlling earthquakes and the dam site we considered finite sources in these computations. We conclude that directivity effects should be taken into account as an important variable in this kind of studies for ground motion characteristics. [ABSTRACT FROM AUTHOR]

In this study, the attenuation of coda waves Q( f) has been estimated for different lapse times and frequencies in the East Anatolian Fault Zone (EAFZ) in Turkey using a single back-scattering model of S-coda envelopes. The data include 255 earthquakes recorded by ten stations. The frequency-dependent Q values are estimated at central frequencies of 1.5, 3, 6, 8, 12, and 18 Hz using 20-30-40 s lapse time windows. Along this fault zone, the frequency-dependent Q obtained for all data and lapse time is Q = 57.5 f. The entire study area is divided into six subregions according to the magnitude of the earthquakes and the location of the fault segments. The estimated average frequency-dependent relation for all lapse times are; $$ Q_{{{\text{c}}_{{\left( {\text{I}} \right)}} }} = 3 4. 3f^{0. 9 3} $$ for Bingöl-Karliova-Erzincan triple junction; $$ Q_{{{\text{c}}_{{\left( {\text{II}} \right)}} }} = 56.3f^{0.71} $$ for Bingol-Lake Hazar segment; $$ Q_{{{\text{c}}_{{\left( {\text{III}} \right)}} }} = 68.5f^{0.75} $$ for Lake Hazar-Sincik segment; $$ Q_{{{\text{c}}_{{\left( {\text{IV}} \right)}} }} = 72.5f^{0.78} $$ Hazar-Sincik and Çelikhan-Gölbaşı faults; $$ Q_{{{\text{c}}_{{\left( {\text{V}} \right)}} }} = 59.7f^{0.87} $$ for Kahramanmaras triple junction and $$ Q_{{{\text{c}}_{{\left( {\text{VI}} \right)}} }} = 67.4f^{0.94} $$ for Amanos Range and Karasu Basin. The lowest Q is determined between Bingol and Malatya. The highest Q value is along Amanos Range. In addition, Q values are calculated for each regions at different lapse times. The average Q value of the study region varies from 53 ± 11 at 1.5 Hz to 498 ± 41 at 18 Hz for 20 s lapse time window, as its variation is from 116 ± 11 at 1.5 Hz to 749 ± 75 at 18 Hz of central frequency for 40 s lapse time window. The increase of Q with lapse times changes from one subregion to another along the fault zone. The rate of increment is significantly higher in Bingöl-Karliova-Erzincan triple junction than in the other subregions. This rapid increase of low Q values in the junction reaches the general attenuation characteristics of the fault at 40 s lapse time. Finally, the low Q and high n values can be attributed to the energy loss as a result of the heterogeneity and activity along the fault zone. The increase of Q with frequency, lapse time may be related to heterogeneity decreases with depth. The rapid increase of Q with depth in Bingöl-Karliova-Erzincan triple junction may be interpreted that the effect of the Northern Anatolian Fault Zone is effective in the upper crust is not so deep compared to EAFZ. [ABSTRACT FROM AUTHOR]

The recently reinvigorated field of infrasonics is poised to provide insight into atmospheric structure and the physics of large atmospheric phenomena, just as seismology has shed considerable light on the workings and structure of Earth's solid interior. Although a natural tool to monitor the atmosphere and shallow Earth for nuclear explosions, it is becoming increasingly apparent that infrasound also provides another means to monitor a suite of natural hazards. The frequent observation of geophysical sources-such as the unsteady sea surface, volcanoes, and earthquakes-that radiate energy both up into the atmosphere and down into the liquid or solid Earth and transmission of energy across Earth's boundaries reminds us that Earth is an interconnected system. This review details the rich history of the unheard sound in the atmosphere and the role that infrasonics plays in helping us understand the Earth system. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a systematic experimental investigation of the effects of buffered particle dampers attached to a multi-degree-of-freedom (mdof) system under different dynamic loads (free vibration, random excitation as well as real onsite earthquake excitations), and analytical/computational study of such a system. A series of shaking table tests of a three-storey steel frame with the buffered particle damper system are carried out to evaluate the performance and to verify the analysis method. It is shown that buffered particle dampers have good performance in reducing the response of structures under dynamic loads, especially under random excitation case. It can effectively control the fundamental mode of the mdof primary system; however, the control effect for higher modes is variable. It is also shown that, for a specific container geometry, a certain mass ratio leads to more efficient momentum transfer from the primary system to the particles with a better vibration attenuation effect, and that buffered particle dampers have better control effect than the conventional rigid ones. An analytical solution based on the discrete element method is also presented. Comparison between the experimental and computational results shows that reasonably accurate estimates of the response of a primary system can be obtained. Properly designed buffered particle dampers can effectively reduce the response of lightly damped mdof primary system with a small weight penalty, under different dynamic loads. [Copyright &y& Elsevier]

The shear wave attenuation field in the lithosphere of Eastern Tien Shan has been mapped. The method based on analysis of the ratio between amplitudes of Sn and Pn waves was used. On aggregate, about 120 seismograms made at the Makanchi station (MKAR), mainly in the period of 2003-2009, at epicentral distances of about 350-1200 km were analyzed. It was found that shear wave attenuation in the lithosphere of Eastern Tien Shan is weaker than that in the region of Central Tien Shan. This agrees with the fact that the rate of deformation of the Earth's crust in Eastern Tien Shan is lower (based on GPS data), as is the seismicity level, in comparison to Central Tien Shan. The zones of high attenuation, where strong earthquakes with M > 7.0 have not occurred for the last 200 years, have been identified: first of all, these are the area west of Urumqi and that of the Lop Nur test site. It is suggested that in the first zone, where an annular seismicity structure has formed over the last 30 years, a strong earthquake may be being prepared. The second zone is most probably related to the uplift of mantle fluids resulting from a long-term intensive technogenic effect, analogous to what has occurred in areas of other nuclear test sites (Nevada and Semipalatinsk). [ABSTRACT FROM AUTHOR]

There are several important wavenumber sampling issues associated with 2.5D seismic modelling in the frequency domain, which need careful attention if accurate results are to be obtained. At certain critical wavenumbers there exist rapid disruptions in the mainly smooth oscillatory spectra. The amplitudes of these disruptions can be very large, and this affects the accuracy of the inverse Fourier transformed frequency-space domain solution. In anisotropic elastic media there are critical wavenumbers associated with each wave mode-the quasi-P (qP) wave, and the two quasi-shear (qS1 and qS2) waves. A small wavenumber sampling interval is desirable in order to capture the highly oscillatory nature of the wavenumber spectrum, especially at increasing distance from the source. Obviously a small wavenumber sampling interval adds greatly to the computational effort because a 2D problem must be solved for every wavenumber and every frequency. The discretisation should be carried out up to some maximum wavenumber, beyond which the field becomes evanescent (exponentially decaying or diffusive). For receivers close to the source, activity persists beyond the critical wavenumber associated with the minimum shear wave velocity in the model. Fortunately, for receivers well removed from the source, the contribution from the evanescent energy is negligible and so there is no need to sample beyond this critical wavenumber. Sampling at Gauss-Legendre spacings is a satisfactory approach for acoustic media, but it is not practical in elastic media due to the difficulty of partitioning the integration around the different critical wavenumbers. We found to our surprise that in transversely isotropic media, the critical wavenumbers are independent of wave direction, but always occur at those wavenumbers corresponding to the maximum phase velocities of the three wave modes (qP, qS1 and qS2), which depend only on the elastic constants and the density. Additionally, we have observed that intermediate layers between source and receiver can filter out to a large degree, the sharp irregularities around the critical wavenumbers in the ω- k spectra. We have found that, using the spectral element method, the singularities (poles) at the critical wavenumbers which exist with analytic solutions, do not arise. However, the troublesome spike-like behaviour still occurs and can be damped out without distorting the spectrum elsewhere, through the introduction of slight attenuation. [ABSTRACT FROM AUTHOR]

Abstract: The first attenuation relationships of peak ground acceleration (PGA) and peak ground velocity (PGV) for northern Vietnam are obtained in this study. Ground motion data are collected by a portable broadband seismic network in northern Vietnam as a part of cooperation between the Institute of Geophysics, Vietnamese Academy of Science and Technology, Vietnam and Institute of Earth Sciences, Academia Sinica, Taiwan. The database comprises a total of 330 amplitude records by 14 broadband stations from 53 shallow earthquakes, which were occurred in and around northern Vietnam in the period between 01/2006 and 12/2009. These earthquakes are of local magnitudes between 1.6 and 4.6, focal depths less than 30km, and epicentral distances less than 500km. The new attenuation relationships for PGA and PGV are: where PGA is in cm/s2, PGV is in cm/s, and R is the epicentral distance in kilometers. The site corrections are also derived in this study. These site corrections are very suitable with the station corrections for ML and imply the qualification of the resulting attenuation relationships. [Copyright &y& Elsevier]

Abstract: Using the single backscattering model a seismic quality factor (Q C), a frequency parameter (n) and an attenuation coefficient (δ) have been studied by analyzing the coda waves of local earthquakes of Baikal rift system. The Q C values were estimated at 6 central frequencies and for 8 lapse time windows W from 20 to 90s. The average Q C varies with frequency from 46±45 (at 0.3Hz) to 1025±221 (at 12Hz). The δ values show significant variations from 0.009km−1 (for W =20s) to 0.003km−1 (for W =90s). Increasing of Q and decreasing of n values with lapse time windows show that the lithosphere upper part is more heterogeneous as against its lower layers. [Copyright &y& Elsevier]

SUMMARY High-resolution 3-D QP and QS models at depths of 0∼14 km in the Longtan reservoir area, which were used to further infer the water infiltration around the reservoir, were constructed by the local earthquake tomography technique. The inversion used t* values measured from velocity spectral amplitudes of 16 134 P-wave and 17 027 S-wave observations of 2828 events recorded by 23 digital seismic stations in the Longtan reservoir area. 3-D QP and QS tomographic images suggest a close relation between the attenuation models and water infiltration. Low QP and QS exist down to 4∼7 km depths beneath the main rivers in the reservoir area, whereas high QP and QS are found both at deep layers and at shallow layers in regions other than the main river area. We inferred that the rocks beneath the main rivers are infiltrated by substantial water and water infiltration reaches 4∼7 km deep, and the ranges of water infiltration vary by region. Specifically, the zone of high water content is estimated to extend up to 10 km away from the Buliu river in the reservoir dam area where water depth in the reservoir reaches maximum, and the extent of water infiltration in rocks can only be about 5 km around from the Hongshui river and the Youla river. Low QP and high QS indicate that the carbonate rocks in the east of the Bala fault area may be saturated with water. Earthquake clusters are mainly concentrated on the low- QP and low- QS zones, indicating that water infiltration beneath the main rivers possibly plays an important role in inducing earthquakes in the Longtan reservoir area. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the attenuation properties of the crust and the quality factor of S wave in eastern Anatolia (Turkey) were determined by local earthquakes for two different areas, Oltu and Erzurum. Seismic wave attenuation can be changed with high pressure or structural effects. Therefore, we argued that the estimation of attenuation coefficient in seismic active zones in Eastern Anatolia is a very useful tool to determine seismic activities. It uses regional waveform data set from two stations, OLT and ERZ, for 95 events that occurred in these regions between 2001 and 2005. The attenuation has been determined using the Chobra–Alexeev model based on the epicenter distance–amplitude relations. This model allows for investigation of the effects of variations in attenuation properties for different areas. We introduced a new magnitude formula for these areas using the amplitude normalization methods for reference values M L=4, so as to correct effects of the magnitudes. We also determined velocity of seismic waves. The average attenuation coefficient (α), average quality factor (Q s) and P and S waves velocities were obtained with normalized amplitude values for Erzurum (ERZ) and Oltu (OLT) as 0.0135km−1, 37, 6.20km/s and 3.38km/s and 0.0151, 34, 6.13 and 3.48. [Copyright &y& Elsevier]

For Anatolian earthquakes, there are insufficient strong motion data from rock sites to model an attenuation relationship for Turkey. This necessitates the use of records from soil sites, which are significantly affected by amplification. In order to include soil site data in the attenuation analyses, boreholes were drilled at 64 recording stations on soil sites. After removing the effects of soil amplification, rock site and soil site data were combined to establish an attenuation relationship. Various models were tested through regression analyses using moment magnitude, epicentral distance and threshold peak horizontal ground acceleration. A new attenuation relationship is modeled for Turkey. [ABSTRACT FROM AUTHOR]

Abstract: Spatial and temporal variations of coda wave attenuation were identified in many studies, and particularly in relation to major earthquakes and volcanic eruptions. Both the coda quality factor, Q c, and its frequency dependence often change following such events, which is often attributed to variations in the properties of large volumes of the subsurface. However, Q c is also strongly sensitive to the assumed theoretical models, which are usually insufficiently accurate for constraining the actual relationships between the geometrical spreading, anelastic dissipation, and scattering. This inaccuracy often leads to significant exaggeration of attenuation effects and complicates the interpretation of temporal variations. To resolve this problem, this study uses a phenomenological approach based on the temporal attenuation coefficient instead of Q c. The attenuation coefficient often linearly depends on frequency f, with intercept related to the geometrical spreading and slope giving the “effective quality” factor Q e as . Two published examples of temporal variations of local-earthquake coda are revisited: a non-volcanic (Stone Canyon in central California) and volcanic area (Mount St. Helens, Washington). In both cases, linear patterns are found, with the effects of γ on coda decay rates being significantly stronger than those of . At Stone Canyon, γ ranged from 0.035 to 0.06s−1 and Q e varied from 3000 to 10,000, with γ increasing and Q e decreasing during the winter season. At Mount St. Helens, γ remained constant at ∼0.18s−1, and Q e changed from 400 before the eruption to 750 after it. The observed temporal variations are explained by the near-surface changes caused by seasonal variations in the non-volcanic case and gas-, magma-, and geothermal-system related in the volcanic case. Scattering attenuation does not appear to be a significant factor in these areas, or otherwise it may be indistinguishable due to its fundamental trade-off with the background structure and anelastic attenuation in the data. [Copyright &y& Elsevier]

In this study the attenuation mechanism of seismic wave energy in north central Italy is estimated using low-magnitude earthquake local data recorded at six stations managed by INGV. Most of the analysed events are located along the Alpine chain in the zone of Iseo and Garda lakes, while a minor part in the Po valley. The zone investigated is characterized by the occurrence of significantly intense earthquakes (magnitude up to 6.6) the most recent occurred in 2004 close to the city of Salò on the coast of the Garda lake ( M= 5.0). Due to the high population density and presence of industrial activity the investigated area is characterized by a high seismic risk. First, the ordinary Multiple Lapse Time Window Analysis (MLTWA) method is applied in the assumption of uniform velocity and scattering and the couple of B, the seismic albedo and , the extinction length inverse (corresponding to the total attenuation coefficient) is calculated in the frequency bands of 1.5, 3, 6 and 12 Hz. To retrieve more realistic estimates, the obtained values of and are corrected taking into account the effects of a depth-dependent earth model, consisting of an earth structure characterized by a transparent upper mantle and a heterogeneous crust. We find that the corrected intrinsic and scattering attenuation parameters (which are proportional to the inverse of the intrinsic/scattering quality factors, and ) are strongly frequency dependent, with a prevalence of scattering attenuation over the intrinsic dissipation. The corrected and uncorrected values of total Q are in agreement with the total Q values obtained with different approaches for the same area. [ABSTRACT FROM AUTHOR]

We investigated the high frequency attenuation of S waves in the southeastern Alps and northern External Dinarides using waveforms from 331 earthquakes (3.0 < M < 6.5). The spectral decay parameter, k, was computed using 1345 three component high quality records, collected by the Italian Strong Motion Network (RAN) and by the Short-Period Seismometric Network of northeastern Italy (NEI) in the period 1976-2007. Weak motion data from 11 stations of the NEI network and strong motion data collected by five accelerometers of the RAN were analysed. The k parameter was estimated in the 0-250 km distance range, in a frequency band extending from the corner frequency of the event up to 25 or 45 Hz, using the amplitude acceleration Fourier spectra of S waves. The observed record-to-record variability of k was modelled by applying a generalized inversion procedure, using both parametric and non-parametric approaches. Our results evidence that k is independent on earthquake size, while it shows both site and distance dependence. Stations of the NEI network present the same increase of k with epicentral distance, R, and show values of the zero-distance k parameter, k( S), between 0.017 and 0.053 s. For the whole region, the k increase with distance can be described through a linear model with slope d k/d R= (1.4 ± 0.1) × 10 s km. Assuming an average S-wave velocity, km s between 5 and 15 km depth, we estimate an average frequency independent quality factor, , for the corresponding crustal layer. The non-parametric approach evidences a weak positive concavity of the curve that describes the k increase with R at about 90 km distance. This result can be approximated through a piecewise linear function with slopes of 1.0 × 10 and 1.7 × 10 s km, in accordance with a three layers model where moving from the intermediate to the bottom layer both and decrease. Two regional dependences were found: data from earthquakes located westward to the NEI network evidence weaker attenuation properties, probably because of S-wave reflections from different parts of the Moho discontinuity under the eastern Po Plain, at about 25-30 km depth, while earthquakes located eastward (in western Slovenia), where the Moho deepens up to 45-50 km, evidence a higher attenuation. Moreover, the k estimates obtained with data from earthquakes located in the area of the 1998 ( M= 5.7) and 2004 ( M= 5.2) Kobarid events are 0.017 s higher than the values predicted for the whole region, probably because of the high level of fracturing that characterizes fault zones. The comparison between measured and theoretical values of k, computed at a few stations with available S-wave velocity profiles, reveals that the major contribution to the total k( S) is due to the sedimentary column (from surface to 800 m depth). The hard rock section contribution is limited to 0.005 s, in accordance with a maximum contribution of 0.010 s predicted by the non-parametric inversion. [ABSTRACT FROM AUTHOR]

Abstract: Body wave studies support the presence of an isotropic layer at the top of the inner core. Recent normal mode models of inner core anisotropy do not contain such a layer, but instead have anisotropic structure extending to the inner core boundary. Here, we use full-coupling of normal mode oscillations sensitive to inner core structure in order to investigate the discrepancy between models of the inner core developed using these two different types of data. We impose an isotropic layer onto existing normal mode models of inner core anisotropy, and calculate frequencies, quality factors and synthetic seismograms for radial modes, PKIKP modes and PKJKP modes. Using full-coupling allows us to make the first simulations of the effect of an isotropic layer on radial modes. The presence of an uppermost isotropic layer has an effect on the frequencies and attenuation of normal modes. By calculating the misfit between data from four large earthquakes and synthetic seismograms created for models of the inner core with isotropic layers of varying thickness, we find that normal mode data are compatible with the presence of an isotropic layer of up to 275km thickness at the top of the inner core. Thus, normal modes can be reconciled with previous body wave studies. The influence of such a layer on PKJKP modes is the only way that S-wave isotropy at the top of the inner core can currently be studied; we show, for the first time, that seismological data support the presence of an S-wave isotropic layer. [Copyright &y& Elsevier]

We derive S-wave attenuation characteristics, earthquake source parameters and site amplification functions at seismic stations used for earthquake early warning in the Irpinia-Basilicata region, using non-parametric spectral inversion of seismograms from 49 local events with M = 1.5-3.1. We obtain relatively low Q values ( Q = 28 at a frequency of 1 Hz) in conjunction with a strong frequency-dependence (close to linear). The source spectra can be satisfactorily modeled using the omega-square model, with stress drops ranging between 0.01-2 MPa, and in the narrow magnitude range available for analysis, the source spectra seem to scale self-similarly. The local magnitude M shows a linear correlation with moment magnitude M, however with a systematic underestimation by about 0.5-magnitude units. The results obtained in this work provide important insights into the ground-motion characteristics that are required for appropriate seismic hazard assessment and are of practical relevance for a suite of applications, such as the calibration of ground-motion prediction equations or the correction for site amplification in earthquake early warning and rapid calculation of shake-maps for seismic emergency management. [ABSTRACT FROM AUTHOR]

Abstract: We have measured 150,000 P and 130,000S wave spectral ratios up to 0.8Hz using recordings of 250 deep (focal depth >200km) earthquakes from 890 global and regional network stations. We have inverted these data to estimate the attenuation parameters tP ⁎ and tS ⁎ for P and S waves and a radial profile of the quality factor Qμ for the lower mantle. On average, tP ⁎ increases by about 0.2s and tS ⁎ increases by about 0.7s between epicentral distances of 30° and 97°. The relatively strong increase of tS ⁎ (ts ≈4tP ⁎) suggests that intrinsic shear attenuation is the cause of the overall trend in our data. The increase of tP ⁎ and tS ⁎ with distance is smaller than predicted by models PREM [12], QL6 [11], and QLM9 [16]. Assuming PREM values for Qμ in the upper mantle, where the data lack resolving power, the P and S wave spectra are explained best if Qμ increases from about 360 at PREM''s 670-km discontinuity to 670 in the lowermost mantle. The high values for Qμ can be reconciled with previously determined values by invoking a frequency-dependence of Qμ(ω) that is proportional to ω0.1. Data that are separated in ‘Pacific’ and ‘circum-Pacific’ subsets have slightly different trends. Estimates of tP ⁎ and tS ⁎ for the Pacific data, which sample the large low shear-velocity province of the Pacific, are higher than the circum-Pacific estimates. Thus, it appears that the Pacific large low shear velocity province has accompanying low Qμ. The difference in Qμ in the lowermost 1000km of the mantle beneath the Pacific and beneath the circum-Pacific is at most 17%. Lateral variations of this magnitude are marginally resolvable given the uncertainties of our measurements. [Copyright &y& Elsevier]

The characteristics of the short-period shear wave attenuation field in the lithosphere of the Turanian Plate, West Tien Shan, Pamir, and Hindu Kush have been studied. The method based on analysis of the logarithm of the ratio between maximal amplitudes of Sn and Pn waves ( Sn/ Pn parameter) has been applied. More than 400 records of earthquakes, obtained at distances of ∼400-1000 km from the AAK digital station, have been processed. It has been found that relatively weak attenuation is observed in the regions of the West Tien Shan and Pamir. The largest area of strong attenuation is located in the region of the Afghan-Tadjik Depression adjacent to Hindu Kush. A wide band of low Sn/ Pn parameter values, stretched northeastwards, has been distinguished. Along with the analogous band of strong attenuation, distinguished before in the regions of Central Tien Shan and Dzungaria, it is the continuation of the largest Chaman Fault, which stretches 850 km along the boundary of the Indian Plate. Source zones of strong earthquakes with M ≥ 7.0 that occurred in the first half of 20th century correspond to relatively weak attenuation. Areas of high attenuation, where strong seismic events have not occurred for the last 110 years, are outlined. Analogously to other seismoactive regions, it is supposed that these areas are related to preparation of strong earthquakes. [ABSTRACT FROM AUTHOR]

Based only on weak-motion data, we carried out a combined study on region-specific source scaling and crustal attenuation in the Central Apennines (Italy). Our goal was to obtain a reappraisal of the existing predictive relationships for the ground motion, and to test them against the strong-motion data [peak ground acceleration (PGA), peak ground velocity (PGV) and spectral acceleration (SA)] gathered during the M 6.15 L'Aquila earthquake (2009 April 6, 01:32 UTC). The L'Aquila main shock was not part of the predictive study, and the validation test was an extrapolation to one magnitude unit above the largest earthquake of the calibration data set. The regional attenuation was determined through a set of regressions on a data set of 12 777 high-quality, high-gain waveforms with excellent S/N ratios (4259 vertical and 8518 horizontal time histories). Seismograms were selected from the recordings of 170 foreshocks and aftershocks of the sequence (the complete set of all earthquakes with M≥ 3.0, from 2008 October 1 to 2010 May 10). All waveforms were downloaded from the ISIDe web page (), a web site maintained by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). Weak-motion data were used to obtain a moment tensor solution, as well as a coda-based moment-rate source spectrum, for each one of the 170 events of the L'Aquila sequence (2.8 ≤ M≤ 6.15). Source spectra were used to verify the good agreement with the source scaling of the Colfiorito seismic sequence of 1997-1998 recently described by . Finally, results on source excitation and crustal attenuation were used to produce the absolute site terms for the 23 stations located within ∼80 km of the epicentral area. The complete set of spectral corrections (crustal attenuation and absolute site effects) was used to implement a fast and accurate tool for the automatic computation of moment magnitudes in the Central Apennines. [ABSTRACT FROM AUTHOR]

The attenuation of seismic waves is one of the basic physical parameters used in seismological studies, which is closely related to the seismicity and tectonic activity of a particular area. In the present study, attenuation properties of the crust beneath the Chedrang Fault and its vicinity, the rupture area of the great Assam earthquake of 12 June 1897 (M = 8.7) are studied using waveforms recorded by a local seismic network composed of five stations. In total 20 local earthquakes have been analysed to estimate (i) coda wave attenuation quality factor (Qc) applying single scattering model, (ii) total attenuation quality factor (Qd) from direct S-wave applying spectral ratio method and (iii) intrinsic and scattering attenuation quality factors (Qi and Qs) following the Wennerberg's approach. Coda Q (Qc) values are obtained using different coda window lengths (20, 30 and 40 s) for frequency bands centred at 1, 1.5, 2, 3, 4, 6, 8, 12, 16 and 18 Hz. This study indicates that Qc increases with increasing lapse time and that Qc is frequency dependent following the attenuation-frequency relation Qc(20) = 36.29 ± 1.18f1.45 ± 0.09, Qc(30) = 69.92 ± 1.11f1.23 ± 0.06 and Qc(40) = 117.08 ± 1.08f1.07 ± 0.05 for 20, 30 and 40 s respectively. This behaviour is usually correlated to the presence of heterogeneity in the crust and to the degree of tectonic complexity underneath the study area. The Qc-1 values for this area follow a substantially similar trend of Qc-1 decay with frequency as the other tectonically active regions of the world. Finally, from the separation of Qs and Qi values, it is observed that the study area can be characterized by a low scattering attenuation (small scattering Q inverse, Qs-1) and by a relatively high intrinsic attenuation (high intrinsic Q inverse, Qi-1). [ABSTRACT FROM AUTHOR]

Abstract: The relative contribution of intrinsic () and scattering () attenuation to seismic wave attenuation was estimated for the Garwhal–Kumaun Himalayas using Multiple Lapse Time Window Analysis (MLTWA) method under the assumption of isotropic scattering. Local earthquake data recorded by an array operated by Wadia Institute of Himalayan Geology (WIHG), India was used for this purpose. It is observed that scattering attenuation primarily contributes to seismic wave attenuation in this region and its value is much higher compared to that of intrinsic attenuation at around 1Hz frequency. As frequency increases the relative contribution of scattering attenuation to total attenuation starts decreasing. However, as seismic albedo is higher than 0.5 for all the frequencies considered, it is concluded that the medium here is highly heterogeneous in nature. [Copyright &y& Elsevier]