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Can a P-wave detection algorithm enhance the performance of an Earthquake Early Warning System (EEWS), particularly in community-engaged networks of low-cost ground motion sensors susceptible to noise? If so, what P-wave detection algorithm would perform the best? This study analyses the performance of four different P-wave detection algorithms using a community-engaged Earthquake Early Warning (EEW) network. The ground motion data from a 48-hour time window around a M5.8 earthquake on 22 September 2022 were used as the basis for this case study, where false and missed detections were analysed for each P-wave detection algorithm. The results indicate that a wavelet transformation-based P-wave picker is the most suitable algorithm for detecting an earthquake with minimal missed and false detections for a community-engaged EEWS. Our results show that a citizen seismology-based EEWS is capable of detecting events of interest to EEW when selecting an appropriate earthquake detection algorithm. The study also suggests future research areas for community-engaged EEWSs, including dynamically changing P-wave detection thresholds and improving citizen seismologists’ user experience and involvement. [ABSTRACT FROM AUTHOR]

Gunung Merapi (Mountain of Fire) is the guardian of a cosmogonic-sacred landscape, and one of the most dangerous volcanoes in the world. Its eruptions are well studied, however, the relationships among ritual, science, protection and grassroots disaster management arising after the 2006 and 2010 eruptions are mostly overlooked. This paper fills this gap in the literature, through qualitative research that explores local perceptions and places respiratory protection in a larger ecology of protective practices during, and after, volcanic crises. In a previous study, 99% of respondents in Yogyakarta used masks to protect from inhaling volcanic ash. In order to understand the respiratory protective practices developed, in the last decade, to cope with Merapi's eruptions, we need to engage with the emergence of the local volunteer-led grassroots monitoring systems. Although these networks were formalised by agencies, they were originally set-up in a bottom-up fashion to respond to pyroclastic flows and other life-threatening volcanic hazards. Our research found that they play a key role in the distribution of masks and respiratory health narratives, thus influencing the wide adoption of certain types of respiratory protection. Disaster management agencies, village heads, ritual experts and volunteers participating in these monitoring networks share spiritual signals (dreams) and scientific ones (seismic data, health narratives) and masks as part of their response to volcanic crises. Our findings about these Merapi networks challenge dominant assumptions in the Disaster Risk Reduction literature that tend to equate building resilience with the substitution of problematic 'cultural beliefs' for 'scientific facts'. [ABSTRACT FROM AUTHOR]

The ground vibrations observed in Taiwan during three teleseismic earthquakes in 2011 by broadband seismometers near major science parks were investigated. Their frequency content was exhibited via spectral analysis, and their effect on structures was examined by response spectra. To assess their possible impact on vibration-sensitive facilities, three vibration criteria in terms of velocity or displacement were utilized. Their predominant frequencies were between 0.04– and 0.16 Hz and somewhat dependent on focal depth and site geology, and they were therefore only influential to very long-period structures. However, the vibration levels exceeded the adopted criteria to some extent, especially at the softer site. [ABSTRACT FROM AUTHOR]

Due to the limited number of seismic records in the soil and inefficient use of one-dimensional wave theory in the estimation of vertical components for seismic waves, this paper studies depth coherency (coherency between the surface seismic waves and that at depth) in order to describe seismic acceleration at different depths based on surface seismic acceleration signals. In this study, the authors utilized data from the KiK network to investigate the variability of seismic ground motions with depth and obtain a model to simulate coherency of depth-dependent ground motions. Furthermore, by using the methodology described in the Chinese Code for the Seismic Design of Buildings, the authors categorized a number of test locations based on the depth and shear velocity of the soil cover. Four different types of sites were defined and both the horizontal and vertical components of ground motion from strong motion seismometers were analyzed. The results show that there is no significant dependence between the estimated coherencies from different earthquake magnitudes or epicentral distance (less than 200 km). Moreover, the behavior of depth coherency is site-dependent and there are notable differences between horizontal and vertical depth coherency. In addition, existing spatial coherency models may not provide a satisfactory estimate of the variation of depth coherency. [ABSTRACT FROM AUTHOR]

Seismic inversion is an effective way to get stress distribution of rock in coal mine, but its usage is still limited by multi-solution problem in practice. As seismometers can only be deployed in limited areas in underground coal mine, it is impossible to solve multi-solution problem by adding more seismometers, thus, we propose a new seismic inversion method which introduces stress value changes as constraint to solve this problem. Numerical experiments show that the new method can reduce the mean distance between inversion results and true wave velocity distributions by about 11.5%, reduce the variance of the distances by about 91%, reduce the mean distance between inversion results and frequency-domain-truncated true wave velocity distributions by about 30.6% and reduce the variance of the distances by about 84.1%. These results indicate that the new method proposed in this paper can reduce the non-uniqueness of solutions in seismic inversion and improve the reliability and stability of seismic inversion. [ABSTRACT FROM AUTHOR]

In this paper, we describe the results of a first pilot experiment of passive seismic monitoring near the active Longqi hydrothermal vent at the Southwest Indian Ridge during Chinese cruise DY115-30. During 102-day experiment, we recorded over 2,000 seismic events on a single ocean bottom seismometer with hydrophone close to the hydrothermal field. We classified these events into the following three classes based on their time–frequency characteristics: (1) volcano tectonic microearthquakes (VTMs); (2) regional earthquakes; (3) short-duration events (SDEs). We preliminarily located the 1,277 VTMs using a single-station location method. Our results revealed hypocenters primarily beneath the axial valley ridge which is about 10 km away from hydrothermal vent and extending to the upper mantle at a depth of 15 km. Two discrete swarms of VTMs occurred during our survey period. The SDEs show a complex frequency characteristics ascribed to clusters of monochromatic waves around different frequencies. This suggests that SDEs result from combination of harmonic waves resonating in fluid-filled pipes and cracks. [ABSTRACT FROM AUTHOR]

The relocation of ocean bottom seismometers (OBSs) is a key step in analyzing the three-dimensional seismic tomographic structure of crust and mantle. In order to get the accurate location of OBSs on the seafloor, we analyze the travel times of direct water waves emitted by air-guns. The Monte Carlo and least square methods have been adopted to calculate the true OBS location. The secondary time correction is necessary if the arrivals of direct water waves show overall time drift during relocation which maybe originates from remnant of linear clock drift correction and average errors of travel time picking, mean water velocity assumption, and experiment geometry. We have improved the original OBS relocation procedure which we used previously for other experiments by deliberateness of a secondary time correction and automatically approaching the really mean water velocity. A series of synthetic tests are carried out firstly to document the feasibility of our procedure and then it is applied on a real experiment. In here, we relocate 28 OBSs in total were relocated in 3D seismic survey near Bashi Channel. Relocation results show that the drifting distances for the 28 OBSs range from 65 to 1136 m between the deployed and relocated locations deduced by relocation results. The Pearson correlation coefficient between OBS drifting direction and sea current direction is 0.79, indicating that the two sets of data are highly linearly related and further manifest the sea current as the most possible driving force for OBS drifting during landing on the seafloor but its detailed influence mechanism is unclear by now. This research is necessary and critical for velocity structure modeling, and the optimal relocation program provides valuable experiences for 3D seismic survey in other area. [ABSTRACT FROM AUTHOR]

This study presents the general features of the structural health monitoring (SHM) system of the long-span cable-supported bridges in Turkey, namely the First Bosphorus Bridge, the Second Bosphorus Bridge (Fatih Sultan Mehmet Bridge), the newly constructed the Third Bosphorus Bridge (Yavuz Sultan Selim) and the Osman Gazi Bridge (Izmit Bay Bridge). Due to the critical function of the bridges in the transportation networks of Istanbul, structural health under extreme and operational load cases without interruption of their operation is essential. The SHM systems are already available and in use for the First and Second Bosphorus Bridges; however, the Yavuz Sultan Selim and the Osman Gazi Bridges, only have the preliminary SHM systems established. General preferences of the current and planned SHM systems of the bridges are given based on the monitoring objectives and requirements. Data collected from the SHM systems are also exhibited as an illustration for structural modal identification of the First Bosphorus Bridge. Based on the experiences from the current SHM systems, future works and planning are recommended to effectively design new SHM system and to efficiently update the current ones. [ABSTRACT FROM AUTHOR]

The seismic background noise is studied at newly constructed sites of the Eastern Ghat Mobile Belts (EGMB), in Orissa. Ten broadband stations have been deployed along two profiles. The area has not been previously attempted for any broadband experiment. To assess the performance of the stations, we investigate the characteristics of different types of noises dominated at those sites. The power spectral densities of ambient background noise for each site are calculated and compared with the global noise model. The results suggest that the noise levels at all stations that belong to profile-1 are within the global high and low bounds. Along profile-2, the station PATN stabilizes after some time post-deployment while noise levels at other two stations are within the proposed limits. Results show that profile-1 is predominated by cultural noise, and the microseismic noise levels are observed to be low in both the profiles. Assessment of the temporal and seasonal variation of the noise has also been done, along with the calculation of the power spectral densities in the East and North components of the seismometer for this station. Overall, our observations suggest that installation of the seismometers have been successful in all the sites. [ABSTRACT FROM AUTHOR]

We conducted single-site and array observations of microtremors in order to revise the shallow subsurface structure of the Furukawa district, Miyagi, Japan, where severe residential damage was reported during the Great Eastern Japan Earthquake of 2011, off the Pacific coast of Tohoku. The phase velocities of Rayleigh waves are estimated from array observations at three sites, and S-wave velocity models are established. The spatial distribution of predominant periods is estimated for the surface layer, on the basis of the spectral ratio of horizontal and vertical components (H/V) of microtremors obtained from single-site observations. We then compared ground motion records from a dense seismometer network with results of microtremor observations, and revised a model of the shallow (~100 m) subsurface structure in the Furukawa district. The model implies that slower near-surface S-wave velocity and deeper basement are to be found in the southern and eastern areas. It was found that the damage in residential structures was concentrated in an area where the average value for the transfer functions in the frequency range of 2 to 4 Hz was large. [ABSTRACT FROM AUTHOR]

The dynamic behaviour of two slender structures with very similar geometry has been investigated in order to evaluate the role played by the construction materials; the comparison has thus been conducted on their vibration properties as resonance frequencies, damping coefficients and mode shapes. The studied structures are two bell towers of a church which were built in two different historical times, with an interval of about one century, using different construction techniques and materials. The experimental tests were carried out by means of output-only measurements of ambient vibration using both contact and non-contact techniques. The signals have been acquired using a tri-directional tromometer or two short period seismometers, both placed in prearranged station points on the structures. Furthermore, the vibrations of the structures have also been measured with the IBIS-S microwave interferometer which is able to provide submillimetric displacements along the radar Line Of Sight without need of any contact with the surface. Therefore, the experimental dynamic response of the church-towers system has been estimated integrating both velocity and displacement data. Though the vibration of the structures had low magnitude, both surveys allowed us to identify the main linear dynamic properties of the structures. Based on these passive surveys, a linear finite element model was calibrated in order to confirm the relationship between the materials and vibration properties. The final model has been locally validated by means ofin situacoustic measurements. [ABSTRACT FROM PUBLISHER]

In this article, we present a novel concept of inertial sensor, based on a linear encoder. Compared to other interferometric sensors, the encoder is much more easy to mount, and the calibration more stable. A prototype has been built and validated experimentally by comparison with a commercial seismometer. It has a resolution of about 10 pm/√Hz. In order to further improve the resolution, two concepts of mechanical amplifiers have been studied and compared. One of them is shown to be extremely promising, provided that the amplifier does not stiffen the sensor. [ABSTRACT FROM AUTHOR]

Resistivity logs have been used by seismic interpreters for many years to construct seismograms, particularly in hydrocarbon gas fields where sonic logs are scarce or absent. The correlation between the conventional synthetic seismogram made from density and sonic logs and the pseudo-synthetic seismogram made from density and resistivity logs has not been very satisfactory in the past because many of the pseudo-synthetic seismograms do not include the ‘gas effect’. Our research team has developed a method to correct for the gas effect, and thereby to improve the overall quality of the pseudo-synthetic seismogram. We apply this method to a well and then compare the improved results to a conventional seismogram made from the same well. Our research should be of interest to researchers in New Zealand, Taiwan and other Pacific Rim countries because of the similarities in the tectonic setting of these nations. [ABSTRACT FROM PUBLISHER]

The frequency content of ground motions seems to be one of the most important parameters to explain the structural damage experienced during worldwide strong earthquakes. The frequency content of ground motions can be characterized by various stochastic and/or deterministic indicators: the frequency bandwidth indicator ϵ (Cartwright & Longuet-Higgins) related to the power spectral density function and, respectively, the control (corner) periodTcof the structural response spectra or the mean periodTM. Peak ground velocity (PGV) and the ratioPGA/PGVcan be used as either damage potential parameters or frequency content indicators. A comparative analysis of stochastic and deterministic frequency content indicators and ofPGVis applied to a set of 30 strong ground motion records having peak ground acceleration (PGA) from 0.2–0.8 g and recorded on 4 continents during the last 70 years. [ABSTRACT FROM PUBLISHER]

The 2009 earthquake-swarm in the Al-Ays volcanic zone in Harrat-Lunayyir in NW Saudi-Arabia is unique because of its intense character and focal-depth distribution at two depth bands (5–10 and 15–20 km) in upper crust without volcanic eruption. We investigate an anatomy of the dyke-intrusion model that supports the mechanism for the swarm itself with seismotectonics, pore pressure diffusion process and inference model. Inferred dyke-intrusion initially started at depth had a five-day peak period (15–20 May 2009) since inception of event-recordings, following which the activity diminished. The process of pore pressure perturbation and resultant “r–tplot” with modelled diffusivity (D = 0.01) relates the diffusion of pore pressure to seismic sequence in a fractured poro-elastic fluid-saturated medium. The spatio-temporal b-values show high b-values (>1.3) along the zone of dyke intrusion (length 10 km and height 5 km) at ∼20km depth. The main-shock and other prominent earthquakes originated on a moderate b-value zone (∼1.0). Temporal b-value analysis indicates an exceptionally low b-value (∼0.4) during the main-shock occurrence. The Al-Ays lava-field is inferred to underlie a seismic volume trending NW-SE bounded on both sides by two NW-SE trending fault systems, dipping 40–50° opposite to each other within a proposed nascent rift setting. [ABSTRACT FROM PUBLISHER]

The Gujarat state seismic network (GSNet), comprising of 50 broadband seismograph (BBS) stations and 40 strong motion accelerographs (SMAs), has been operated and maintained by the Institute of Seismological Research (ISR) since 2006. Nineteen permanent BBS stations are connected through VSAT and the rest are kept in an offline mode. The local geology beneath seismic stations varies from Mesozoic to Quaternary formations. The seismic background noise (SBN) at these stations was calculated and found that it varies widely as a function of period, time and geographic location. We have studied the SBN variation along these three parameters for 14 online BBS stations of the GSNet. It was found that the stations located on the Deccan trap and Mesozoic formations are good sites with low SBN while stations on Quaternary, Tertiary and soft soil are noisy. The comparison between day and night noise spectra shows that SBN increases during the daytime at most of the stations. Three typical noisy peaks at three different periods were recorded at all of the stations, which is a global phenomenon. The results of this study will be helpful in selecting sites for future earthquake observations. [ABSTRACT FROM AUTHOR]

An analysis of boulders displaced during the September 2010 MW 7.1 Darfield (Canterbury) earthquake provides non-instrumental constraints on the variability, distribution and origin of strong ground motion during major earthquakes. Boulders ranging in mass from 10 to 5000 kg were displaced 8–970 cm laterally from hosting soil sockets of <1 cm to 50 cm depth at several sites in the Port Hills, roughly 35 km southeast of the earthquake epicentre. Boulder displacement was observed on N-striking (000–015°) ridges above c. 400 m elevation but not on NE-, NW- and SE-striking ridges. The prevailing boulder horizontal displacement azimuth of 250±20° is subparallel with the direction of instrumentally recorded transient peak ground horizontal displacements. Boulder displacement distance has no correlation with displacement azimuth, boulder mass or soil socket depth and has a partial correlation with slope angle. The lateral displacement of many boulders from low slope (<10°) ground surfaces on ridge crests exceeds nearby instrumentally recorded peak ground displacements at lower elevations by up to an order of magnitude, implying that seismic waves were amplified at the study sites. Preliminary 2-D FLAC modelling suggests that topographic amplification may explain this observation. The co-existence of displaced and non-displaced boulders at proximal (<1 m spacing) sites also suggests small-scale ground motion variability and/or varying boulder-ground dynamic interactions relating to shallow phenomena such as variability in soil depth, bedrock fracture density and/or microtopography on the bedrock–soil interface. Remapping of boulders following the February 2011 MW 6.2 Christchurch earthquake reveals no subsequent relocation despite locally recorded horizontal and vertical ground accelerations well in excess of the Darfield earthquake and pervasive rockfalls and landslides elsewhere. This study successfully identifies some of the major controls on spatial ground motion variability at non-instrumented locations and highlights the complexity of ground response at different spatial scales and for different earthquake characteristics. [ABSTRACT FROM AUTHOR]

The first four months of aftershocks of the Darfield earthquake have been studied using data from temporary and permanent seismic stations to investigate the fault geometry, stress field and evolution of seismicity and seismic properties. Earthquake relocations illuminate fault segments and show that the majority of aftershocks occurred beyond the areas of highest slip during the Darfield earthquake. Seismic anisotropy shows a mixture of fast directions parallel to the maximum horizontal stress and fault-parallel fast directions. This, combined with the lack of observable growth of seismicity along fault segments, suggests that the Greendale Fault broke a pre-existing fault plane. [ABSTRACT FROM AUTHOR]

The purpose of this activity is to inform students about earthquakes and their movements and to give students an idea of how a seismograph works. Even though students may not experience an actual earthquake, the hands-on activity of creating a seismograph will give students an opportunity to visually explore concepts related to earthquakes. [ABSTRACT FROM AUTHOR]

Northwestern Italian weak-motion data were used to study attenuation characteristics of horizontal peak ground acceleration (PGA) and horizontal peak ground velocity (PGV) from earthquakes of local magnitudes (Ml) up to 5.1. Data have been provided by the RSNI (Regional seismic network of Northwestern Italy) and RSLG (Regional seismic network of Lunigiana-Garfagnana) waveform database. The database consists of more than 14 000 horizontal components recorded in the period 1999–2002 by both broadband and enlarged band seismometers. The accuracy of the procedure used to extract PGA values from the velocity recordings was verified comparing observed and derived PGA values at station STV2, which was equipped with both a temporary K2 Kinemetrics accelerometer and Guralp CMG40 broadband sensor. The attenuation of both peak ground acceleration and peak ground velocity was found to be logarithmically distributed with a strong attenuation for low distances (less than 50 km) and low Ml values (<3.0). The resulting equations are: \begin{eqnarray*} {\rm Log(PGA)} & = & - 3.19 + 0.87 M - 0.042 M^2 - 1.92\ {\rm Log}(R) + 0.249S\,,\\[5pt] {\rm Log(PGA)} & = & - 4.23 + 0.76 M - 0.018 M^2 - 1.56\ {\rm Log}(R) + 0.230S\,, \end{eqnarray*} where PGA is expressed in g, PGV is expressed in m/s, M is local magnitude, R is the hypocentral distance in kilometers and S is a dummy variable assuming values of 0 and 1 for rock and soil respectively. For increasing distance and magnitude, both PGA and PGV values show a linear distribution. The validity range of the obtained attenuation relationships is 0–200 km for distances and Ml up to 4.5. Sensitivity studies performed by analysis of residuals, showed that predicted PGA and PGV values are stable with respect to reasonable variations of the model and distances providing the data. Comparisons with attenuation relationships proposed for Italian region, derived from strong motion records, are also presented. [ABSTRACT FROM AUTHOR]

This article focuses on the role of seismology within geophysics. Seismology has little statistical history before the development of the Milne-Shaw seismograph in the 1890s. Somewhat earlier the theory of wave propagation in an elastic medium had been worked out, a qualitative intensity scale for assessing ground motion had been developed, and there had been attempts to compile lists of large historical earthquakes. Although the New Zealand Alpine Fault marks a major plate boundary, it has been a seismically quite zone ever since Europeans arrived about 2 centuries ago. Water level changes have long been touted as an earthquake precursor. The 1989 Loma Prieta earthquake was widely felt and caused moderate damage; it did not, however, break the surface. Matsu'ura studied the forecasting of large aftershocks using Ogata's techniques, based on ETAS model for detecting precursory relative quiescence. A key theoretical issue is the tussle between rebound-type arguments, suggesting characteristic earthquakes at regular intervals, and the G-R law, suggesting extreme irregularity. Recent work has focused on reviewing the applicability of catalog-based prediction methods to New Zealand data.

The article discusses seismographs that were taken by Rice University researchers to examine possible reasons why some parts of the Colorado Plateau are rising while parts of the lower crust are falling.