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The casualties and financial losses caused by large earthquakes have led to an awareness of prediction importance of such earthquakes. The earthquake prediction is divided into four categories: long term, intermediate term, short term, and immediate. The M8 algorithm is one of the intermediate-term middle-range prediction algorithms primarily used to predict earthquake of magnitude 8 or more and is applied later for smaller magnitudes. The Iranian Plateau is less exposed to earthquake with magnitude 8 or more and it is observed that the seismicity rate in this region is generally low. Thus; the original M8 is not suitable for applying in this region. The objective of this study is to modify the M8 algorithm for Prediction of Major M7.0+ Earthquakes in the Iranian Plateau. The major earthquake of magnitude 7 or more in the Iranian plateau from 1975 to 2018 is considered as the target earthquakes. The hit rate times 1 minus alarm rate is defined as objective function and the particles swarm optimization meta-heuristic algorithm is used to maximize it. The optimum M8 could predict 14 out of 17 large earthquakes in the Iranian plateau while occupying 31.7% of the spatio-temporal space as the alarm. The results show that by employing an optimization algorithm, we can modify the M8 algorithm for efficient prediction of the target magnitudes less than 8 in the regions with low seismicity rate. [ABSTRACT FROM AUTHOR]

The present study estimates source parameters and proposes scaling relationships for moderate size earthquakes (mb 3.7-5.8) in seismically active North-East India region. The study is based upon the spectral analysis of high-quality waveforms comprising of P- and S-waves obtained from strong ground motion (SMA) records of 50 earthquakes that has occurred in the region. A two-step procedure is adopted to estimate the earthquake source parameters. It has been observed that the average seismic moment and source radii vary from 1.05 × 1015 to 1.99 × 1017 N-m and 500 to 2000 m, respectively. The average corner frequency ratio [fC(P)/fC(S)] of P-wave and S-wave is found to be 1.2, which shows the shift in the corner frequency. The total estimated energy varies between 9.22 × 1010 and 1.42 × 1014 J, while the average stress drop varies from 1.8 to 29.4 MPa. One of the major outcome of this study is that the stress drop does not vary significantly with the magnitude and self-similarity exist among the earthquakes in North-East India region. The scaling relation between the seismic moment and the corner frequency is Mofc3=1.35×1017N- ms-3. The median stress drop value for NE India region is found to be about 9.2 MPa. The earthquake source parameters and the scaling relations developed in this study will be useful for carrying scenario based seismic hazard analysis studies in the NE India region. [ABSTRACT FROM AUTHOR]

Site response analysis is conducted at 37 seismic stations located in the Gauteng, North West and Free State provinces in South Africa, using the Nakamura H/V spectral ratio technique on records of the Orkney 5 August 2014 earthquake. The earthquake, of magnitude ML = 5.5, led to the unfortunate death of one person and damage of more than 600 houses. Intensity data collected soon after the event showed that the effects of the earthquake appeared to vary significantly across the region. This motivated the authors to conduct a more detailed investigation of the effects of site conditions on seismic station records in the region. Resonance frequency values obtained from the H/V ratios were observed to vary strongly across the region and also within seismic station clusters. Similar behaviour was observed with the peak amplitude of the ratios at the resonance frequency, except for the Johannesburg area whose results showed a relatively simple shape of the ratios implying less complex velocity structure. All the H/V ratios exhibit dominant peaks at resonant frequencies that varied between 0.5 and 35 Hz. The average observed resonant frequency was f = 7.9 Hz. The amplitude of the dominant peaks also varied strongly from 1.66 to 11.69, with only two sites exhibiting maximum peaks with amplitude smaller than 2. These results serve as a strong motivation or justification for the on-going microzonation studies in South Africa, where a detailed study of the velocity structure will be used to obtain reliable information on site amplification and resonance. [ABSTRACT FROM AUTHOR]

In this paper, we report the co-seismic temperature response of the Ms6.3 Kangding earthquake in Sichuan, China, which occurred within a bedrock temperature monitoring station network constructed in the east of the Qinghai-Tibet Plateau. Results indicate that two kinds of co-seismic responses of bedrock temperature, exponential and step-rise ones, were recorded at different stations. As for the former, the amplitude of co-seismic response is about 5.6-11.5 mK (the average value is 7.33 mK), while the latter is about 0.31-0.98 mK (the average value is 0.52 mK). These two kinds of responses would be indicative of the two different mechanisms for change in temperature. On the one hand, the exponential responses represent the effects of fluid advection along the borehole wall, which are associated with a finite quantity of heat produced by earthquake-driven transient fluid flow. The step-rise responses, on the other hand, represent the direct response of temperature to change in the crustal stress accompanying with earthquake. We still tested relationship between stress variation and temperature response on the rock samples taken from the boreholes, and the average value is 0.77 mK/MPa. Upon thus, these step-rise temperature responses imply that co-seismic change in mean stress is about 0.40 MPa. We simplify effects of fluid by presuming a one-dimensional model where the flow is either up or down based on a pressure change due to compression or tension. The stress state, compression or tension, deduced by the direction of the fluid flow is qualitatively accordant with the direct response of bedrock temperature to stress change. In summary, characteristic changes in bedrock temperature occurred coincidentally with the earthquake at different stations, agreeing generally with regional stress adjustments accompanying the earthquake. Changes in bedrock temperature do seem to offer a useful means of monitoring dynamic changes in shallow crustal stress. [ABSTRACT FROM AUTHOR]

We analyzed earthquakes of sequences that occurred at different times near San Carlos, a town of approximately 5000 inhabitants. The seismic sequences happened during March-April 1989, October 2000-June 2001, and 5-15 February 2004 at about 200 km west of the Pacific-North America plate boundary. The strong shaking from initial earthquakes of the first two sequences prompted the installation of temporary seismic stations in the area. With data recorded by these stations, we found an earthquake distribution that is consistent with the northwest segment of the Santa Margarita fault. Both the focal depth, that seemed to increase in E-NE direction, and a composite fault-plane solution, obtained from polarity data of the small earthquakes, were also consistent with the main characteristics of that fault. We also found that our normal-faulting mechanism (east side down) was quite similar to centroid moment tensor solutions for earthquakes with M 5.4 and 5.3 that occurred in the area in February 2004. It is likely, then, that these larger earthquakes also occurred along the Santa Margarita Fault. To get some insight into the regional stress pattern, we compared the above mechanisms with mechanisms reported for other earthquakes of the Pacific margin of Baja California Sur and the Gulf of California regions. We observed that focal mechanisms of the two regions have T axes of stress that plunge sub horizontally in E-NE average direction. The corresponding P axes have N-NW average trend, but for the Pacific earthquakes these axes plunge at angles that are ~35° larger than those for the Gulf earthquakes. These more vertically inclined P axes of compressive stress mean substantial oblique fault motions. The mixture of oblique and strike-slip components of fault motions, as the focal mechanisms show, confirms a transtensional stress regime for the region. Before this research, we knew little about the seismicity and styles of faulting in the area. Now we know that earthquakes can occur along the coastline of Baja California, at 60 km east of the Tosco-Abreojos fault system. We conclude that transtensional deformation is taking place across a wide zone of the Pacific margin of Baja California. Finally, we point out that although the studied earthquakes were of small magnitude, they might serve as a reminder of the danger that future larger events pose to San Carlos. [ABSTRACT FROM AUTHOR]

The collision between the Arabian and Eurasian plates in eastern Turkey causes the Anatolian block to move westward. The North Anatolian Fault (NAF) is a major strike-slip fault that forms the northern boundary of the Anatolian block, and the Erzincan Basin is the largest sedimentary basin on the NAF. In the last century, two large earthquakes have ruptured the NAF within the Erzincan Basin and caused major damage ( M = 8.0 in 1939 and M = 6.8 in 1992). The seismic hazard in Erzincan from future earthquakes on the NAF is significant because the unconsolidated sedimentary basin can amplify the ground motion during an earthquake. The amount of amplification depends on the thickness and geometry of the basin. Geophysical constraints can be used to image basin depth and predict the amount of seismic amplification. In this study, the basin geometry and fault zone structure were investigated using broadband magnetotelluric (MT) data collected on two profiles crossing the Erzincan Basin. A total of 24 broadband MT stations were acquired with 1-2 km spacing in 2005. Inversion of the MT data with 1D, 2D and 3D algorithms showed that the maximum thickness of the unconsolidated sediments is ~3 km in the Erzincan Basin. The MT resistivity models show that the northern flanks of the basin have a steeper dip than the southern flanks, and the basin deepens towards the east where it has a depth of 3.5 km. The MT models also show that the structure of the NAF may vary from east to west along the Erzincan Basin. [ABSTRACT FROM AUTHOR]

In seismically active regions, faults nucleate, propagate, and form networks that evolve over time. To simulate crustal faulting processes, including the evolution of fault-zone properties, a rheological model must incorporate concepts such as damage rheology that describe the various stages of the seismic cycle (strain localization, subcritical crack growth and macroscopic failure) while accounting for material degradation and healing and off-fault deformation. Here we study the fundamental patterns of strain-localisation within the framework of a continuum damage rheology by performing a shear band analysis (linear instability analysis) and comparing predictions of shear band orientations with numerical results of the nonlinear problem. We find (analytically and numerically) that the angle between the shear band and the less compressive (transverse) direction is between 47° in compression tests with a strain ratio of 0.25 (highly confined compression test), and 60° for a strain ratio higher than 1.4 (axial compression and transverse extension). In addition we find that shear bands exhibit local dilation ( I > 0) in a wide range of strain ratios excluding only simulations with highly confined compression (which yield compacting shear bands or non-localized deformation). Finally, we discuss the applicability of the damage model for simulating deformation in the seismogenic, brittle crust. [ABSTRACT FROM AUTHOR]

Although the evidence for complexity is overwhelming, the dynamics of faulting is still poorly understood. Whilst it has long been known that discreteness in numerical earthquake models produces complexity, the mathematical structure and form of this complexity has never been fully established. Using a simple 1D nonlinear fault model we show how complexity can arise in discrete models through the presence of nonlinear, scale-dependent (or mesh-dependent) terms. We show that scale-dependencies may be a significant factor in the generation of slip complexity and pulse-like rupture over multiple earthquake cycles. We demonstrate that the introduction of length scales in discrete earthquake models implies that both strongly weakening friction and scale-dependent processes may be necessary in generating the pulse-like rupture mode and earthquake complexity over multiple earthquake cycles. [ABSTRACT FROM AUTHOR]

We have developed a new, unified modeling technique for the total simulation of seismic waves, ocean acoustic waves, and tsunamis resulting from earthquakes, based on a finite difference method simulation of the 3D equations of motion. Using the equilibrium between the pressure gradient and gravity in these equations, tsunami propagation is naturally incorporated in the simulation based on the equations of motion. The performance of the parallel computation for the newly developed tsunami-coupled equations using a domain partitioning procedure shows a high efficiency coefficient with a large number of CPU cores. The simulation results show how the near-field term associated with seismic waves produced by shallow earthquakes leads to a permanent coseismic deformation of the ground surface, which gives rise to the initial tsunami on the sea surface. Propagation of the tsunami along the sea surface as a gravity wave, and ocean acoustic waves in seawater with high-frequency multiple P-wave reflections between the free surface and sea bottom, are also clearly demonstrated by the present simulations. We find a good agreement in the tsunami waveform between our results and those obtained by other simulations based on an analytical model and the Navier-Stokes equations, demonstrating the effectiveness of the tsunami-coupling simulation model. Based on this simulation, we show that the ratio of the amplitude of ocean acoustic waves to the height of the tsunami, both of which are produced by the earthquake, strongly depends on the rise time of the earthquake rupture. This ratio can be used to obtain a more detailed understanding of the source rupture processes of subduction zone earthquakes, and for implementing an improved tsunami alert system for slow tsunami earthquakes. [ABSTRACT FROM AUTHOR]

We investigated the development of a distinct later phase observed at stations near the Japan Trench associated with shallow, outer-rise earthquakes off the coast of Sanriku, northern Japan based on the analysis of three-component broadband seismograms and FDM simulations of seismic wave propagation using a heterogeneous structural model of the Japan Trench subduction zone. Snapshots of seismic wave propagation obtained through these simulations clearly demonstrate the complicated seismic wavefield constructed by a coupling of the ocean acoustic waves and the Rayleigh waves propagating within seawater and below the sea bottom by multiple reflections associated with shallow subduction zone earthquakes. We demonstrated that the conversion to the Rayleigh wave from the coupled ocean acoustic waves and the Rayleigh wave as they propagate upward along the slope of seafloor near the coast is the primary cause of the arrival of the distinct later phase at the station near the coast. Through a sequence of simulations using different structural models of the Japan Trench subduction zone, we determined that the thick layer of seawater along the trench and the suddenly rising sea bottom onshore of the Japanese island are the major causes of the distinct later phase. The results of the present study indicate that for realistic modeling of seismic wave propagation from the subduction zone earthquakes, a high-resolution bathymetry model is very crucial, although most current simulations do not include a water column in their simulation models. [ABSTRACT FROM AUTHOR]

We explore fractal properties of two observed seismicity distributions prior to the 2003 M 7.4 Colima, Mexico and 1992 M 7.3 Landers, USA earthquakes, together with several mathematical fractal distributions and two non-fractal ones, in order to estimate minimum reliable sample sizes, determine whether fractality for observed seismicity is essentially different from random uniform distributions, and explore the possibility of extracting premonitory information from fractal characteristics of seismicity before large earthquakes. Sample sizes above 800 events for whole catalogs appear to be sufficient to maintain ordered multifractality and to yield dimension estimates that vary smoothly and reliably. Fractal estimates appear to be best for whole catalogs that include aftershocks. The fractal characteristics of spatial distributions of seismicity are essentially different from those of the uniform random distribution, which is the null hypothesis of a non-fractal distribution with minimum information. The fractal dimensions and afractality measures of seismicity distributions change with time and show distinctive behaviors associated with foreshocks and main events, although these behaviors are different for each example. Results suggest the possibility of a priori identification of foreshocks to large earthquakes. A combination of fractal dimension and afractality measures over time may be helpful in large earthquake premonitory studies. [ABSTRACT FROM AUTHOR]

Romania is an earthquake prone area with a few destructive earthquakes per century. The National Institute for Earth Physics carries out the seismic survey of Romania through the Romanian National Seismic Network (RNSN) consisting of 65 real-time seismic stations. Daily reports and monthly bulletins are delivered after routinely analyzing and processing the recorded data. In the present paper we applied the Seismic Network Evaluation through Simulation method for the RNSN configuration as it was in August 2011 to estimate the background noise level, assess the appropriateness of the velocity model adopted in routine location procedure, evaluate the hypocenter location uncertainty and determine the detection magnitude threshold. Areas of greater (southern Romania) and lower (Carpathians and Apuseni Mountains) background noise within the RNSN are identified by mapping the average power of noise in 1-12 Hz frequency range. The statistical study of the P and S phases residual times allow us to assess the appropriateness of the velocity model used in routine location. Both P- and S-wave velocity models can be optimized to improve the quality of the hypocenter location. As shown by our analysis, the RNSN is able to detect and locate earthquakes with M magnitude above 2.5 anywhere on the Romanian territory, except the border areas, such as the Crisana-Maramures seismic source zone. Merging data from both sides of the border significantly improves the quality of hypocenter location in these areas. [ABSTRACT FROM AUTHOR]

Rigorous predictability experimentation requires a statistical characterization of the performance metric used to evaluate the participating models. We explore the properties of the area skill score measure and consider issues related to experimental discretization. For the case of continuous alarm functions and continuous observations, we present exact analytical solutions that describe the distribution of the area skill score for unskilled predictors, and we also describe how a Gaussian distribution with known mean and variance can be used to approximate the area skill score distribution. We quantify the deviation of the exact distribution from the Gaussian approximation by specifying the kurtosis excess as a function of the number of observed target earthquakes. For numerical earthquake predictability experiments that involve discretization of the study region and observations, we explore simulation procedures for estimating the area skill score distribution, and we present efficient algorithms for various experimental scenarios. When more than one target earthquake occurs within a given space/time/magnitude bin, the probabilities of predicting individual events are not independent, and this requires special consideration. Having presented the statistical properties of the area skill score, we describe and illustrate a preliminary procedure for comparing earthquake prediction strategies based on alarm functions. [ABSTRACT FROM AUTHOR]

The Region–Time–Length (RTL) algorithm has been applied to different instrumental catalogues to detect seismic quiescence before medium-to-large earthquakes in Italy in the last two decades. RTL performances are sensitive to the choice of spatial and temporal parameters. The method for automatic parameters selection developed by Chen and Wu has been applied to twelve Italian earthquakes with magnitude greater than 5. The limits of the method in constructing maps of seismic quiescence before the earthquake are demonstrated, and a simple improvement is proposed. Then a new technique, namely RTL, is proposed for routine surveys of the Italian seismicity. RTL has been applied to all the earthquakes with magnitude greater than 4 in the Italian area in the time interval 1994–2004; four different sub-areas have been identified, with different characteristics in the level of recorded seismicity. One subarea—Tyrrhenian Sea—was characterized by a too low level of recorded seismicity for the application of the method. In the other three subareas a seismic quiescence was detected before at least the 66% of the earthquakes with magnitude greater or equal to 4 and all the earthquakes with magnitude greater than 5. [ABSTRACT FROM AUTHOR]

In weather forecasting, current and past observational data are routinely assimilated into numerical simulations to produce ensemble forecasts of future events in a process termed “model steering”. Here we describe a similar approach that is motivated by analyses of previous forecasts of the Working Group on California Earthquake Probabilities (WGCEP). Our approach is adapted to the problem of earthquake forecasting using topologically realistic numerical simulations for the strike-slip fault system in California. By systematically comparing simulation data to observed paleoseismic data, a series of spatial probability density functions (PDFs) can be computed that describe the probable locations of future large earthquakes. We develop this approach and show examples of PDFs associated with magnitude M > 6.5 and M > 7.0 earthquakes in California. [ABSTRACT FROM AUTHOR]

systematic analysis is made of static Coulomb stress changes and earthquake occurrence in the area of the North Aegean Sea, Greece, in order to assess the prospect of using static stress changes to construct a regional earthquake likelihood model. The earthquake data set comprises all events of magnitude M ≥ 5.2 which have occurred since 1964. This is compared to the evolving stress field due to constant tectonic loading and perturbations due to coseismic slip associated with major earthquakes (M ≥ 6.4) over the same period. The stress was resolved for sixteen fault orientation classes, covering the observed focal mechanisms of all earthquakes in the region. Analysis using error diagrams shows that earthquake occurrence is better correlated with the constant tectonic loading component of the stress field than with the total stress field changes since 1964, and that little, if any, information on earthquake occurrence is lost if only the maximum of the tectonic loading over the fault orientation classes is considered. Moreover, the information on earthquake occurrence is actually increased by taking the maximum of the evolving stress field since 1964, and of its coseismic-slip component, over the fault orientation classes. The maximum, over fault orientation classes, of linear combinations of the tectonic loading and the evolving stress field is insignificantly better correlated with earthquake occurrence than the maximum of the tectonic loading by itself. A composite stress-change variable is constructed from ordering of the maximum tectonic loading component and the maximum coseismic-slip component, in order to optimize the correlation with earthquake occurrence. The results indicate that it would be difficult to construct a time-varying earthquake likelihood model from the evolving stress field that is more informative than a time-invariant model based on the constant tectonic loading. [ABSTRACT FROM AUTHOR]

If aseismic slip occurs on a fault or its deeper extension, both seismicity and crustal deformation around the source would be affected. Anomalous phenomena of this kind are revealed from earthquake occurrence data and geodetic records during a period of 10 years leading up to the March 2005 M 7.0 earthquake west of Fukuoka that occurred off the northern coast of Kyushu, Japan. Seismicity rate anomalies (quiescence and activation) took place relative to the rates expected by the ETAS model in a number of seismic zones in and around the Kyushu District. The seismic zone of the relative quiescence and activation consistently corresponds to the zone of the negative and positive ΔCFS (Coulomb failure stress change), respectively, assuming the precursory aseismic slips on the M 7.0 source fault. In addition, we consider the time series of geodetic baseline distances between permanent GPS stations in the Kyushu District for the same period, which also supports the possible precursory slips rather than the known slow slips beneath the Bungo Straight, off the eastern coast of Kyushu. [ABSTRACT FROM AUTHOR]

Western Turkey has a long history of destructive earthquakes that are responsible for the death of thousands of people and which caused devastating damage to the existing infrastructures, and cultural and historical monuments. The recent earthquakes of Izmit (Kocaeli) on 17 August, 1999 ( M = 7.4) and Düzce ( M = 7.2) on 12 November, 1999, which occurred in the neighboring fault segments along the North Anatolian Fault (NAF), were catastrophic ones for the Marmara region and surroundings in NW Turkey. Stress transfer between the two adjacent fault segments successfully explained the temporal proximity of these events. Similar evidence is also provided from recent studies dealing with successive strong events occurrence along the NAF and parts of the Aegean Sea; in that changes in the stress field due to the coseismic displacement of the stronger events influence the occurrence of the next events of comparable size by advancing their occurrence time and delimiting their occurrence place. In the present study the evolution of the stress field since the beginning of the twentieth century in the territory of the eastern Aegean Sea and western Turkey is examined, in an attempt to test whether the history of cumulative changes in stress can explain the spatial and temporal occurrence patterns of large earthquakes in this area. Coulomb stress changes are calculated assuming that earthquakes can be modeled as static dislocations in elastic half space, taking into account both the coseismic slip in large ( M ≥ 6.5) earthquakes and the slow tectonic stress buildup along the major fault segments. The stress change calculations were performed for strike-slip and normal faults. In each stage of the evolutionary model the stress field is calculated according to the strike, dip, and rake angles of the next large event, whose triggering is inspected, and the possible sites for future strong earthquakes can be assessed. A new insight on the evaluation of future seismic hazards is given by translating the calculated stress changes into earthquake probability using an earthquake nucleation constitutive relation, which includes permanent and transient effects of the sudden stress changes. [ABSTRACT FROM AUTHOR]

We associate waveform-relocated background seismicity and aftershocks with the 3-D shapes of late Quaternary fault zones in southern California. Major earthquakes that can slip more than several meters, aftershocks, and near-fault background seismicity mostly rupture different surfaces within these fault zones. Major earthquakes rupture along the mapped traces of the late Quaternary faults, called the principal slip zones (PSZs). Aftershocks occur either on or in the immediate vicinity of the PSZs, typically within zones that are ±2-km wide. In contrast, the near-fault background seismicity is mostly accommodated on a secondary heterogeneous network of small slip surfaces, and forms spatially decaying distributions extending out to distances of ±10 km from the PSZs. We call the regions where the enhanced rate of background seismicity occurs, the seismic damage zones. One possible explanation for the presence of the seismic damage zones and associated seismicity is that the damage develops as faults accommodate bends and geometrical irregularities in the PSZs. The seismic damage zones mature and reach their finite width early in the history of a fault, during the first few kilometers of cumulative offset. Alternatively, the similarity in width of seismic damage zones suggests that most fault zones are of almost equal strength, although the amount of cumulative offset varies widely. It may also depend on the strength of the fault zone, the time since the last major earthquake as well as other parameters. In addition, the seismic productivity appears to be influenced by the crustal structure and heat flow, with more extensive fault networks in regions of thin crust and high heat flow. [ABSTRACT FROM AUTHOR]

In 2006, we started construction of an observation network of 12 stations in and around Shikoku and the Kii Peninsula to conduct research for forecasting Tonankai and Nankai earthquakes. The purpose of the network is to clarify the mechanism of past preseismic groundwater changes and crustal deformation related to Tonankai and Nankai earthquakes. Construction of the network of 12 stations was completed in January 2009. Work on two stations, Hongu-Mikoshi (HGM) and Ichiura (ICU), was finished earlier and they began observations in 2007. These two stations detected strain changes caused by the slow-slip events on the plate boundary in June 2008, although related changes in groundwater levels were not clearly recognized. [ABSTRACT FROM AUTHOR]

In this paper, we present a model for studying aftershock sequences that integrates Coulomb static stress change analysis, seismicity equations based on rate-state friction nucleation of earthquakes, slip of geometrically complex faults, and fractal-like, spatially heterogeneous models of crustal stress. In addition to modeling instantaneous aftershock seismicity rate patterns with initial clustering on the Coulomb stress increase areas and an approximately 1/t diffusion back to the pre-mainshock background seismicity, the simulations capture previously unmodeled effects. These include production of a significant number of aftershocks in the traditional Coulomb stress shadow zones and temporal changes in aftershock focal mechanism statistics. The occurrence of aftershock stress shadow zones arises from two sources. The first source is spatially heterogeneous initial crustal stress, and the second is slip on geometrically rough faults, which produces localized positive Coulomb stress changes within the traditional stress shadow zones. Temporal changes in simulated aftershock focal mechanisms result in inferred stress rotations that greatly exceed the true stress rotations due to the main shock, even for a moderately strong crust (mean stress 50 MPa) when stress is spatially heterogeneous. This arises from biased sampling of the crustal stress by the synthetic aftershocks due to the non-linear dependence of seismicity rates on stress changes. The model indicates that one cannot use focal mechanism inversion rotations to conclusively demonstrate low crustal strength (≤10 MPa); therefore, studies of crustal strength following a stress perturbation may significantly underestimate the mean crustal stress state for regions with spatially heterogeneous stress. [ABSTRACT FROM AUTHOR]

The New Zealand Earthquake Forecast Testing Centre is being established as one of several similar regional testing centres under the umbrella of the Collaboratory for the Study of Earthquake Predictability (CSEP). The Centre aims to encourage the development of testable models of time-varying earthquake occurrence in the New Zealand region, and to conduct verifiable prospective tests of their performance over a period of five or more years. The test region, data-collection region and requirements for testing are described herein. Models must specify in advance the expected number of earthquakes with epicentral depths h ≤ 40 km in bins of time, magnitude and location within the test region. Short-term models will be tested using 24-h time bins at magnitude M ≥ 4. Intermediate-term models and long-term models will be tested at M ≥ 5 using 3-month, 6-month and 5-year bins, respectively. The tests applied will be the same as at other CSEP testing centres: the so-called N test of the total number of earthquakes expected over the test period; the L test of the likelihood of the earthquake catalogue under the model; and the R test of the ratio of the likelihoods under alternative models. Four long-term, three intermediate-term and two short-term models have been installed to date in the testing centre, with tests of these models commencing on the New Zealand earthquake catalogue from the beginning of 2008. Submission of models is open to researchers worldwide. New models can be submitted at any time. The New Zealand testing centre makes extensive use of software produced by the CSEP testing centre in California. It is envisaged that, in time, the scope of the testing centre will be expanded to include new testing methods and differently-specified models, nonetheless that the New Zealand testing centre will develop in parallel with other regional testing centres through the CSEP international collaborative process. [ABSTRACT FROM AUTHOR]

Predictions of earthquakes worldwide by the M8-MSc algorithm, which defines locations of Times of Increased Probability (TIPs), have been tested for nearly two decades, and the authors claim a high rate of success. Thus, it might be appropriate to ask what the consequences in terms of human losses may be if the expected earthquakes should occur. The loss estimating tool QUAKELOSS also has been tested in real-time mode during the last five years with success. Therefore, it is reasonable to estimate the order of magnitude of human losses if great earthquakes should occur in TIPs. Here I compare the consequences if M 8.5 earthquakes should happen in the current TIPs of southern Sumatra and central Chile (K ossobokov and S oloviev, , centers at 4.75S/102.625E and 31.25S/71.77 W, respectively). The selection of the attenuation function is calibrated by matching theoretically calculated intensities and fatalities to the observed values in historic earthquakes. In both areas, the standard attenuation function I use is applicable. The results show that in southern Sumatra fatalities are expected to number fewer than 1,000 (possibly as much as a factor of 5 fewer), whereas they are likely to be larger than 1,000 (possibly as much as a factor six) in central Chile. These figures, however, do not account for possible tsunami effects. The difference is due to two factors. The earthquake sources are farther offshore, and there are only small settlements along the coast in southern Sumatra, whereas along the Chilean coast, large harbor cities are located in the northern part of the TIP area. Regardless of TIP predictions, large earthquakes are to be expected along the Chilean coast. Therefore, it seems advisable to implement mitigating measures in La Serena and Coquimbo, where most of the victims are expected. [ABSTRACT FROM AUTHOR]

Precursory swarms associated with major earthquakes in the Western Nepal Himalaya and its adjoining region (bounded by 28.0°–31.0°N and 79.5°–82.2°E) have been studied using seismicity data from 1963 to 2006. The delineation of preparation zones for future seismic disturbances is carried out using the temporal and the spatial distribution of earthquakes, considering the events with cutoff magnitude mb ≥ 4.3 in four anomalous episodes: normal/background (N); anomalous/swarm (A); precursory gap (G) and main shock sequence (M), respectively. Five cases of anomalous seismicity have been identified, including two cases for which quiescence episodes still continue. Three moderate earthquakes of 1980 ( mb 6.1, Bajhang), 1984 ( mb 5.6, Bajura) and 1999 ( mb 6.6, Chamoli) in Western Nepal and its adjoining Indian region were preceded by well-defined patterns of anomalous seismicity/precursory swarm. Two additional cases of anomalous seismicity patterns were observed: (1) 1999–2006, and (2) 2003–2006. In these two cases no main shock has yet occurred. However, the seismicity from 1999 onwards has fluctuated from low to high to low, as in the precursory sequences for previous earthquakes. The occurrence of the swarm sequence followed by a quiescence phase, which is still continuing, is an indication of a precursory seismicity gap in the region. From the predictive equations developed for the Himalayan frontal arc, it is estimated that an earthquake of M 6.5 ± 0.5 may occur at any time up to 2011 in an area bounded by 29.3°–30.5°N and 81.2°–81.9°E, in the focal depth range 10–30 km. [ABSTRACT FROM AUTHOR]

We present a simple method for long- and short-term earthquake forecasting (estimating earthquake rate per unit area, time, and magnitude). For illustration we apply the method to the Pacific plate boundary region and the Mediterranean area surrounding Italy and Greece. Our ultimate goal is to develop forecasting and testing methods to validate or falsify common assumptions regarding earthquake potential. Our immediate purpose is to extend the forecasts we made starting in 1999 for the northwest and southwest Pacific to include somewhat smaller earthquakes and then adapt the methods to apply in other areas. The previous forecasts used the CMT earthquake catalog to forecast magnitude 5.8 and larger earthquakes. Like our previous forecasts, the new ones here are based on smoothed maps of past seismicity and assume spatial clustering. Our short-term forecasts also assume temporal clustering. An important adaptation in the new forecasts is to abandon the use of tensor focal mechanisms. This permits use of earthquake catalogs that reliably report many smaller quakes with no such mechanism estimates. The result is that we can forecast earthquakes at higher spatial resolution and down to a magnitude threshold of 4.7. The new forecasts can be tested far more quickly because smaller events are considerably more frequent. Also, our previous method used the focal mechanisms of past earthquakes to estimate the preferred directions of earthquake clustering, however the method made assumptions that generally hold in subduction zones only. The new approach escapes those assumptions. In the northwest Pacific the new method gives estimated earthquake rate density very similar to that of the previous forecast. [ABSTRACT FROM AUTHOR]

We extend existing branching models for earthquake occurrences by incorporating potentially important estimates of tectonic deformation and by allowing the parameters in the models to vary across different tectonic regimes. We partition the Earth’s surface into five regimes: trenches (including subduction zones and oceanic convergent boundaries and earthquakes in outer rise or overriding plate); fast spreading ridges and oceanic transforms; slow spreading ridges and transforms; active continental zones, and plate interiors (everything not included in the previous categories). Our purpose is to specialize the models to give them the greatest possible predictive power for use in earthquake forecasts. We expected the parameters of the branching models to be significantly different in the various tectonic regimes, because earlier studies ( Bird and Kagan in Bull Seismol Soc Am 94(6):2380–2399, ) found that the magnitude limits and other parameters differed between similar categories. We compiled subsets of the CMT and PDE earthquake catalogs corresponding to each tectonic regime, and optimized the parameters for each, and for the whole Earth, using a maximum likelihood procedure. We also analyzed branching models for California and Nevada using regional catalogs. Our estimates of parameters that can be compared to those of other models were consistent with published results. Examples include the proportion of triggered earthquakes and the exponent describing the temporal decay of triggered earthquakes. We also estimated epicentral location uncertainty and rupture zone size and our results are consistent with independent estimates. Contrary to our expectation, we found no dramatic differences in the branching parameters for the various tectonic regimes. We did find some modest differences between regimes that were robust under changes in earthquake catalog and lower magnitude threshold. Subduction zones have the highest earthquake rates, the largest upper magnitude limit, and the highest proportion of triggered events. Fast spreading ridges have the smallest upper magnitude limit and the lowest proportion of triggered events. The statistical significance of these variations cannot be assessed until methods are developed for estimating confidence limits reliably. Some results apparently depend on arbitrary decisions adopted in the analysis. For example, the proportion of triggered events decreases as the lower magnitude limit is increased, possibly because our procedure for assigning independence probability favors larger earthquakes. In some tests we censored earthquakes occurring near and just after a previous event, to account for the fact that most such earthquakes will be missing from the catalog. Fortunately the branching model parameters were hardly affected, suggesting that the inability to measure immediate aftershocks does not cause a serious estimation bias. We compare our branching model with the ETAS model and discuss the differences in the models parametrization and the results of earthquake catalogs analysis. [ABSTRACT FROM AUTHOR]

A long-range correlation between earthquakes is indicated by some phenomena precursory to strong earthquakes. Most of the major earthquakes show prior seismic activity that in hindsight seems anomalous. The features include changes in regional activity rate and changes in the pattern of small earthquakes, including alignments on unmapped linear features near the (future) main shock. It has long been suggested that large earthquakes are preceded by observable variations in regional seismicity. Studies on seismic precursors preceding large to great earthquakes with M ≥ 7.5 were carried out in the northeast India region bounded by the area 20°–32°N and 88°–100°E using the earthquake database from 1853 to 1988. It is observed that all earthquakes of M ≥ 7.5, including the two great earthquakes of 1897 and 1950, were preceded by abnormally low anomalous seismicity phases some 11–27 years prior to their occurrence. On the other hand, precursory time periods ranged from 440 to 1,768 days for main shocks with M 5.6–6.5 for the period from 1963 to 1988. Furthermore, the 6 August, 1988 main shock of M 7.5 in the Arakan Yoma fold belt was preceded by well-defined patterns of anomalous seismicity that occurred during 1963–1964, about 25.2 years prior to its occurrence. The pattern of anomalous seismicity in the form of earthquake swarms preceding major earthquakes in the northeast India region can be regarded as one of the potential seismic precursors. Database constraints have been the main barrier to searching for this precursor preceding smaller earthquakes, which otherwise might have provided additional information on its existence. The entire exercise indicates that anomalous seismicity preceding major shocks is a common seismic pattern for the northeast India region, and can be employed for long-range earthquake prediction when better quality seismological data sets covering a wide range of magnitudes are available. Anomalous seismic activity is distinguished by a much higher annual frequency of earthquake occurrence than in the preceding normal and the following gap episodes. [ABSTRACT FROM AUTHOR]

The concept of background seismicity is strictly related to the identification of spontaneous and triggered earthquakes. The definition of foreshocks, main shocks and aftershocks is currently based on procedures depending on parameters whose values are notoriously assumed by subjective criteria. We propose a method for recognizing the background and the induced seismicity statistically. Rather than using a binary distinction of the events in these two categories, we prefer to assign to each of them a probability of being independent or triggered. This probability comes from an algorithm based on the ETAS model. A certain degree of subjectivity is still present in this procedure, but it is limited by the possibility of adjusting the free parameters of the algorithm by rigorous statistical criteria such as maximum likelihood. We applied the method to the seismicity of southern California and analyzed the sensitivity of the results to the free parameters in the algorithm. Finally, we show how our statistical declustering algorithm may be used for mapping the background seismicity, or the moment rate in a seismic area. [ABSTRACT FROM AUTHOR]

We present estimates of future earthquake rate density (probability per unit area, time, and magnitude) on a 0.1-degree grid for a region including California and Nevada, based only on data from past earthquakes. Our long-term forecast is not explicitly time-dependent, but it can be updated at any time to incorporate information from recent earthquakes. The present version, founded on several decades worth of data, is suitable for testing without updating over a five-year period as part of the experiment conducted by the Collaboratory for Study of Earthquake Predictability (CSEP). The short-term forecast is meant to be updated daily and tested against similar models by CSEP. The short-term forecast includes a fraction of our long-term one plus time-dependent contributions from all previous earthquakes. Those contributions decrease with time according to the Omori law: proportional to the reciprocal of the elapsed time. Both forecasts estimate rate density using a radially symmetric spatial smoothing kernel decreasing approximately as the reciprocal of the square of epicentral distance, weighted according to the magnitude of each past earthquake. We made two versions of both the long- and short-term forecasts, based on the Advanced National Seismic System (ANSS) and Preliminary Determinations of Epicenters (PDE) catalogs, respectively. The two versions are quite consistent, but for testing purposes we prefer those based on the ANSS catalog since it covers a longer time interval, is complete to a lower magnitude threshold and has more precise locations. Both forecasts apply to shallow earthquakes only (depth 25 km or less) and assume a tapered Gutenberg-Richter magnitude distribution extending to a lower threshold of 4.0. [ABSTRACT FROM AUTHOR]

We have applied a variation of the Epidemic Type Aftershock Sequence (ETAS) model, which is a stochastic triggering epidemic model incorporating short-term clustering, to data collected by the New Zealand Seismological Observatory-Wellington (Geonet) for forecasting earthquakes of moderate and large magnitude in the New Zealand region. The model uses earthquake data only, with no explicit use of tectonic, geologic, or geodetic information. In this epidemic-type model every earthquake is regarded, at the same time, as being triggered by previous events and triggering following earthquakes. A maximum likelihood estimate of the model parameters has been performed on the learning period from 1960 to 2005 for earthquakes of magnitude 4.0 and larger. Forecast verification procedures have been carried out in a forward-retrospective way on the January 2006 to April 2008 data set, making use of statistical tools as the log-likelihood ratio, the Relative Operating Characteristics (ROC) diagrams, the Molchan error diagrams, the probability gain and the R-score. These procedures show that the clustering epidemic model achieves a log-likelihood ratio per event of the order of some units, and a probability gain up to several hundred times larger than a time-independent spatially uniform random forecasting hypothesis. The results show also that a significant component of the probability gain is linked to the time-independent spatial distribution of the seismicity used in the model. [ABSTRACT FROM AUTHOR]

Recently the equilibrium property of ergodicity was identified in an earthquake fault system (T iampo et al., Phys. Rev. Lett. 91, 238501, ; Phys. Rev. E 75, 066107, ). Ergodicity in this context not only requires that the system is stationary for these networks at the applicable spatial and temporal scales, but also implies that they are in a state of metastable equilibrium, one in which the ensemble averages can be substituted for temporal averages when studying their behavior in space and time. In this work we show that this property can be used to identify those regions of parameter space which are stationary when applied to the seismicity of two naturally-occurring earthquake fault networks. We apply this measure to one particular seismicity-based forecasting tool, the Pattern Informatics index (T iampo et al., Europhys. Lett. 60, 481–487, ; R undle et al., Proc. National Acad. Sci., U.S.A., Suppl. 1, 99, 2463, ), in order to test the hypothesis that the identification of ergodic regions can be used to improve and optimize forecasts that rely on historic seismicity catalogs. We also apply the same measure to synthetic catalogs in order to better understand the physical process that affects this accuracy. We show that, in particular, ergodic regions defined by magnitude and time period provide more reliable forecasts of future events in both natural and synthetic catalogs, and that these improvements can be directly related to specific features or properties of the catalogs that impact the behavior of their spatial and temporal statistics. [ABSTRACT FROM AUTHOR]

We construct a single hazard function from multiple predictive parameters independently developed for moderate earthquakes in Kanto, Japan, during a learning period from 1990 to 1999, and applied to a testing period from 2000 to 2005. Here, we consider as predictive parameters the a and b values of the Gutenberg–Richter relation, the ν value (change in b value), and the Every Earthquake a Precursor According to Scale (EEPAS) model rate. To study the correlations among the parameters, we prepare two groups of space–time coordinate sets for assessment, namely the background and conditional groups selected from the learning period. The background group contains ten thousand sets of coordinates randomly selected from the space–time volume of our study. The conditional group contains 33 sets of space–time coordinates corresponding to the epicenters of the target earthquakes ( M ≥ 5.0) just before their times of occurrence. Each parameter for the background group is transformed so that its distribution conforms to the standard Normal function. The mean and variance of the conditional distribution is then estimated after applying the same transformation to the conditional group. Using the means and variances of b values, ν values and EEPAS rates and the correlation matrices in the background and conditional distributions, we construct a combined hazard function following the procedure developed for normally distributed parameters. The information gain per event ( IGpe) of the new hazard function is 0.26 and 0.3 units larger than that of the EEPAS rate for the learning and testing period, respectively. The R-test confirms the statistical significance of the difference in the IGpe value for the testing period. [ABSTRACT FROM AUTHOR]

An Annual Consultation on the Likelihood of Earthquakes is regularly undertaken in continental China. It is a special kind of intermediate-term medium-range earthquake forecast and a practical service provided by seismological communities within the capability of modern seismology. One of the problems the Annual Consultation encounters is its false alarm rate, which has been higher than expected and has caused numerous controversies on the methodology and significance of the Annual Consultation. To tackle this problem we use the concept of reverse tracing of precursors (RTP) to analyze the long-term seismic activity in the alarm regions, or regions thought to have increased probability of earthquakes, as identified by the Annual Consultation. We apply the Pattern Informatics (PI) and relative intensity (RI) algorithms to the long-term estimation of seismic hazard in the RTP analysis. A retrospective study of the Sichuan-Yunnan region of southwest China, using the data from 1990 to 2003, shows that, by choosing the threshold proportion of overlapped areas between the long-term estimates and the Annual Consultation, the RTP analysis can correctly remove some of the false-alarm regions from the “black list’ and thus reduce the false-alarm rate of the Annual Consultation, without reducing the hit rate. Remarkably, the RTP approach, although originally proposed for short-term earthquake predictions, seems able to contribute to the Annual Consultation as well. [ABSTRACT FROM AUTHOR]

A brief account is given of the principles of stochastic modelling in seismology, with special regard to the role and development of stochastic models for seismicity. Stochastic models are seen as arising in a hierarchy of roles in seismology, as in other scientific disciplines. At their simplest, they provide a convenient descriptive tool for summarizing data patterns; in engineering and other applications, they provide a practical way of bridging the gap between the detailed modelling of a complex system, and the need to fit models to limited data; at the most fundamental level they arise as a basic component in the modelling of earthquake phenomena, analogous to that of stochastic models in statistical mechanics or turbulence theory. As an emerging subdiscipline, statistical seismology includes elements of all of these. The scope for the development of stochastic models depends crucially on the quantity and quality of the available data. The availability of extensive, high-quality catalogues and other relevant data lies behind the recent explosion of interest in statistical seismology. At just such a stage, it seems important to review the underlying principles on which statistical modelling is based, and that is the main purpose of the present paper. [ABSTRACT FROM AUTHOR]

In the southernmost Kuril Trench, the tsunami source regions vary their along-trench extent even among earthquakes occurring within the same segment. Recent studies suggest that the tsunami source of the 1952 Tokachi-oki earthquake (M 8.1) differs from but partially overlaps with that of the 2003 Tokach-oki earthquake (M 8.0). Furthermore, the along-trench extent among the earthquakes seems to differ between deep and shallow portions of the subduction interface. A seismic gap has been recognized along the deep subduction interface between the sources of the 1952 and 1973 earthquakes. We propose that the gap is now larger, including both shallow to deep portions of the interface between the 1973 and 2003 earthquakes. Variability in spatial extent of large subduction earthquakes in both along-trench direction and trench-normal direction makes it difficult to forecast future earthquakes in the southernmost Kuril Trench. [ABSTRACT FROM AUTHOR]

The Gujarat and adjoining region falls under all four seismic zones V, IV, III and II of the seismic zoning map of India, and is one of the most seismically prone intracontinental regions of the world. It has experienced two large earthquakes of magnitude M w 7.8 and 7.7 in 1819 and 2001, respectively and several moderate earthquakes during the past two centuries. In the present study, the probability of occurrence of earthquakes of M ≥ 5.0 has been estimated during a specified time interval for different elapsed times on the basis of observed time intervals between earthquakes using three stochastic models namely, Weibull, Gamma and Lognormal. A complete earthquake catalogue has been used covering the time interval of 1819 to 2006. The whole region has been divided into three major seismic regions (Saurashtra, Mainland Gujarat and Kachchh) on the basis of seismotectonics and geomorphology of the region. The earthquake hazard parameters have been estimated using the method of maximum likelihood. The logarithmic of likelihood function (ln L) is estimated and used to test the suitability of models in three different regions. It was found that the Weibull model fits well with the actual data in Saurashtra and Kachchh regions, whereas Lognormal model fits well in Mainland Gujarat. The mean intervals of occurrence of earthquakes are estimated as 40.455, 20.249 and 13.338 years in the Saurashtra, Mainland Gujarat and Kachchh region, respectively. The estimated cumulative probability (probability that the next earthquake will occur at a time later than some specific time from the last earthquake) for the earthquakes of M ≥ 5.0 reaches 0.9 after about 64 years from the last earthquake (1993) in Saurashtra, about 49 years from the last earthquake (1969) in Mainland Gujarat and about 29 years from the last earthquake (2006) in the Kachchh region. The conditional probability (probability that the next earthquake will occur during some specific time interval after a certain elapsed time from last earthquake) is also estimated and it reaches about 0.8 to 0.9 during the time interval of about 57 to 66 years from the last earthquake (1993) in Saurashtra region, 31 to 51 years from the last earthquake (1969) in Mainland Gujarat and about 21 to 28 years from the last earthquake (2006) in Kachchh region. [ABSTRACT FROM AUTHOR]

In this paper, ground motion during the Independence Day earthquake of August 15, 1950 (Mw 8.6, B en-M enahem et al., 1974) in the northeastern part of India is estimated by seismological approaches. A hybrid simulation technique which combines the low frequency ground motion simulated from an analytical source mechanism model with the stochastically simulated high-frequency components is used for obtaining the acceleration time histories. A series of ground motion simulations are carried out to estimate the peak ground acceleration (PGA) and spectral accelerations at important cities and towns in the epicentral region. One sample PGA distribution in the epicentral region encompassing the epicenter is also obtained. It is found that PGA in the epicentral region has exceeded 1 g during this earthquake. The estimated PGA’s are validated to the extent possible using the MMI values. The simulated acceleration time histories can be used for the assessment of important engineering structures in northeastern India. [ABSTRACT FROM AUTHOR]

There are two fundamentally different approaches to assessing the probabilistic risk of earthquake occurrence. The first is fault based. The statistical occurrence of earthquakes is determined for mapped faults. The applicable models are renewal models in that a tectonic loading of faults is included. The second approach is seismicity based. The risk of future earthquakes is based on the past seismicity in the region. These are also known as cluster models. An example of a cluster model is the epidemic type aftershock sequence (ETAS) model. In this paper we discuss an alternative branching aftershock sequence (BASS) model. In the BASS model an initial, or seed, earthquake is specified. The subsequent earthquakes are obtained from statistical distributions of magnitude, time, and location. The magnitude scaling is based on a combination of the Gutenberg-Richter scaling relation and the modified Båth’s law for the scaling relation of aftershock magnitudes relative to the magnitude of the main earthquake. Omori’s law specifies the distribution of earthquake times, and a modified form of Omori’s law specifies the distribution of earthquake locations. Unlike the ETAS model, the BASS model is fully self-similar, and is not sensitive to the low magnitude cutoff. [ABSTRACT FROM AUTHOR]

The US NOAA/NWS tsunami warning centers have relied on earthquake location and depth, and scalar measures of earthquake size and slowness to assess the potential for the generation of a destructive tsunami by an earthquake. Recent earthquakes, such as Peru 2001, Sumatra 2004 and the Java 2006, manifest some of the difficulties the warning centers face as they try to cope with unusual earthquakes. We have undertaken a study of a simple teleseismic waveform inverse model and applied it to the earthquakes of June 23, 2001 in Peru and of July 17, 2006 in Java. Synthetic numerical experiments suggest that the most salient features of the rupture history of an earthquake can be recovered. Furthermore the calculations can be conducted quickly enough to be useful in a warning center context. We have applied our technique to the Peru 2001 and recent Java 2006 earthquakes. Our overall results are consistent with those obtained from other studies. The results show why the Peru event initially looked slow to the US tsunami warning centers and that the Java event is a truly slow or tsunami earthquake. Clearly, the warning centers stand to benefit from an increased understanding of the earthquakes they monitor. Furthermore, better knowledge of the slip distribution along a fault will improve tsunami wave-height forecasts. [ABSTRACT FROM AUTHOR]

Earthquakes in Iran and neighbouring regions are closely connected to their position within the geologically active Alpine-Himalayan belt. Modern tectonic activity is forced by the convergent movements between two plates: The Arabian plate, including Saudi Arabia, the Persian Gulf and the Zagros Ranges of Iran, and the Eurasian plate. The intensive seismic activity in this region is recorded with shallow focal depth and magnitude rising as high as Mw = 7.8. The study region can be attributed to a highly complex geodynamic process and therefore is well suited for multifractal seismicity analysis. Multifractal analysis of earthquakes (mb ≥ 3) occurring during 1973 – 2006 led to the detection of a clustering pattern in the narrow time span prior to all the large earthquakes: Mw = 7.8 on 16.9.1978; Mw = 6.8 on 26.12.2003; Mw = 7.7 on 10.5.97. Based on the spatio-temporal clustering pattern of events, the potential for future large events can be assessed. Spatio-temporal clustering of events apparently indicates a highly stressed region, an asperity or weak zone from which the rupture propagation eventually nucleates, causing large earthquakes. This clustering pattern analysis done on a well-constrained catalogue for most of the fault systems of known seismicity may eventually aid in the preparedness and earthquake disaster mitigation. [ABSTRACT FROM AUTHOR]

The 2004 Indian Ocean tsunami caused an estimated 230,000 casualties, the worst tsunami disaster in history. A similar-sized tsunami in the Pacific Ocean, generated by the 1960 Chilean earthquake, commenced international collaborations on tsunami warning systems, and in the tsunami research community through the Tsunami Commission of International Union of Geodesy and Geophysics. The IUGG Tsunami Commission, established in 1960, has been holding the biannual International Tsunami Symposium (ITS). This volume contains selected papers mostly presented at the 22nd ITS, held in the summer of 2005. This introduction briefly summarizes the progress of tsunami and earthquake research as well as international cooperation on tsunami warning systems and the impact of the 2004 tsunami. Brief summaries of each paper are also presented. [ABSTRACT FROM AUTHOR]

The 2004 Sumatra-Andaman tsunami was recorded by hydrophones of the International Monitoring System at Site H08 near Diego Garcia, notably in frequency bands extending outside the range of the Shallow Water Approximation. Despite the severe high-pass filtering involved in this instrumentation, we show that the spectral amplitudes recovered around T = 87 s can be successfully explained by generation from the seismic source, in the framework of the normal mode theory of tsunami excitation. At the lower frequencies characteristic of more conventional tsunami waves (800 to 3200 s), the signal is probably present in the hydrophone records, but reliable deconvolution of its spectral amplitude is precluded by the fact that the instrumental filters lowered the tsunami signal to the level of resolution of the instrument digitizer. In the context of distant tsunami warning, hydrophone records could provide useful insight into high-frequency tsunami components, and even at lower, more conventional, frequencies, provided that an unfiltered channel could be recorded routinely. [ABSTRACT FROM AUTHOR]

Volcán de Colima, the most active volcano in Mexico, had a climactic episode on 20 November, 1998. On this date, a dome formed on the small summit crater during the previous few days, collapsed generating block-and-ash flows. The event was preceded by almost twelve months of seismic activity, which continued afterwards for several more months. We analyzed the main seismic activity, which occurred from 20 March, 1998 to 31 March, 1999. The seismicity was dominated by volcano-tectonic earthquakes before the climax, and subsequently by hybrid and long-period earthquakes. We determined the frequency of events for the entire period, and located most of the volcano-tectonic events. To assess the possibility that these earthquakes were generated by the same source, they were tested for their similitude through cross correlation in the time domain. Six groups of similar events, or earthquake families, were generated. The members of these families appeared before the 20 November event, apparently ceasing afterwards. We examined the location of the families' events with respect to an existing gravity model in which an anomalous body of negative density contrast suggests the presence of the magma chamber. Most of the family events occur on top of the anomalous body, which suggests they were associated with the passage of magma through the feeding conduits of the volcano. [ABSTRACT FROM AUTHOR]

In heterogeneous brittle media, the evolution of damage is strongly influenced by the multiscale coupling effect. To better understand this effect, we perform a detailed investigation of the damage evolution, with particular attention focused on the catastrophe transition. We use an adaptive multiscale finite-element model (MFEM) to simulate the damage evolution and the catastrophic failure of heterogeneous brittle media. Both plane stress and plane strain cases are investigated for a heterogeneous medium whose initial shear strength follows the Weibull distribution. Damage is induced through the application of the Coulomb failure criterion to each element, and the element mesh is refined where the failure criterion is met. We found that as damage accumulates, there is a stronger and stronger nonlinear increase in stress and the stress redistribution distance. The coupling of the dynamic stress redistribution and the heterogeneity at different scales result in an inverse cascade of damage cluster size, which represents rapid coalescence of damage at the catastrophe transition. [ABSTRACT FROM AUTHOR]

Active faults are commonly associated with spatially anomalously high concentrations of soil gases such as carbon dioxide and Rn, suggesting that they are crustal discontinuities with a relatively high vertical permeability through which crustal and subcrustal gases may preferably escape towards the earth's surface. Many earthquake-related hydrologic and geochemical temporal changes have been recorded, mostly along active faults especially at fault intersections, since the 1960s. The reality of such changes is gradually ascertained and their features well delineated and fairly understood. Some coseismic changes recorded in ``near field'' are rather consistent with poroelastic dislocation models of earthquake sources, whereas others are attributable to near-surface permeability enhancement. In addition, coseismic (and postseismic) changes were recorded for many moderate to large earthquakes at certain relatively few ``sensitive sites'' at epicentral distances too large (larger for larger earthquakes, up to 1000 km or more for magnitude 8) to be explained by the poroelastic models. They are probably triggered by seismic shaking. The sensitivity of different sites can be greatly different, even when separated only by meters. The sensitive sites are usually located on or near active faults, especially their intersections and bends, and characterized by some near-critical hydrologic or geochemical condition (e.g., permeability that can be greatly increased by a relatively small seismic shaking or stress increase). Coseismic changes recorded for different earthquakes at a sensitive site are usually similar, regardless of the earthquakes' location and focal mechanism. The sensitivity of a sensitive site may change with time. Also pre-earthquake changes were observed hours to years before some destructive earthquakes at certain sensitive sites, some at large epicentral distances, although these changes are relatively few and less certain. Both long-distance coseismic and preseismic changes call for more realistic models than simple elastic dislocation for explanation. Such models should take into consideration the heterogeneity of the crust where stress is concentrated at certain weak points (sensitive sites) along active faults such that the stress condition is near a critical level prior to the occurrence of the corresponding earthquakes. To explain the preseismic changes, the models should also assume a broad-scaled episodically increasing strain field. [ABSTRACT FROM AUTHOR]

The occurrence of the Algiers earthquake ( M 6.8) of May 21, 2003, has motivated the necessity to reassess the probabilistic seismic hazard of northern Algeria. The fact that this destructive earthquake took place in an area where there was no evidence of previous significant earthquakes, neither instrumental nor historical, strongly encourages us to review the seismic hazard map of this region. Recently, the probabilistic seismic hazard of northern Algeria was computed using the spatially smoothed seismicity methodology. The catalog used in the previous computation was updated for this review, and not only includes information until June 2003, but also considers a recent re-evaluation of several historical earthquakes. In this paper, the same methodology and seismicity models are utilized in an effort to compare this methodology against an improved and updated seismic catalog. The largest mean peak ground acceleration (PGA) values are obtained in northernmost Algeria, specifically in the central area of the Tell Atlas. These values are of the order of 0.48 g for a return period of 475 years. In the City of Algiers, the capital of Algeria, and approximately 50 km from the reported epicenter of this latest destructive earthquake, a new mean PGA value of 0.23 g is obtained for the same return period. This value is 0.07 g greater than that obtained in the previous computation. In general, we receive greater seismic hazard results in the surrounding area of Algiers, especially to the southwest. The main reason is not this recent earthquake by itself, but the significant increase in the mmax magnitude in the seismic source where the city and the epicenter are included. [ABSTRACT FROM AUTHOR]

An evaluation of the magnitude of historical earthquakes is proposed, through an empirical relation based on a felt area of historical earthquakes derived from a vectorial modelling of macroseismic intensity distribution. [ABSTRACT FROM AUTHOR]

Many ancient structures such as temples were constructed on the basis of a very strict plan and excellent workmanship. For this reason, even their slight deformation due to various effects (ground instability, earthquake oscillations, etc.) can be identified, and it is possible to discriminate between different types of deformation due to earthquakes and those due to other natural causes or to anthropogenic effects. Two study cases are presented here: the Propylaia on the Acropolis and the temple of Hephaistos (Hephaisteion) in the Agora at Athens. In both buildings deformation was produced by earthquakes. [ABSTRACT FROM AUTHOR]

- It has long been realized that the linear Gutenberg-Richter model arduously describes the frequency-magnitude relationship for the magnitude span ranging from small to large earthquakes because of the breakdown of the self-similarity rule due to the cha [ABSTRACT FROM AUTHOR]

- Earthquake faultings have a wide variety of slip behaviors, such as, a log-linear frequency-magnitude relation, characteristic earthquakes, slow slip events, and so on. We report a model which can reproduce a certain variety of observed complex slip behaviors on a fault. Our 3-D model simulates the seismic cycle on a shallow dipping subduction fault in a homogeneous elastic half-space, on which frictional sliding is controlled by a rate- and state-dependent friction law. We find that the behaviors of reproduced seismic cycles depend on a lateral dimension of a seismogenic zone (H) with respect to a constant seismogenic width in dip direction (W). The following three domains appear in the seismic cycle behaviors: (1) Regular, periodic behaviors whenHis comparable toW; (2) transitional, quasi-periodic behaviors whenH/W~ 3; and (3) complex behaviors whenH/Wis larger than about 4. The slip behavior in the domain (1) is characterized by a periodical recurrence of a characteristic earthquake, which is centered in strike direction. In the domain (2), although earthquakes are still centered, these recurrence intervals and the sizes are modulated within a certain range. Also, in the domain (3), earthquakes occur not only at the center but at various lateral positions on the seismogenic zone. In this domain, the log-linear frequency-magnitude relations, like the Gutenberg-Richter relation, are produced. Slow slip events also occur at source areas of the earthquakes. It is suggested that a heterogeneous stress distribution at a source region is important, as well as heterogeneities in friction properties on the fault, for understanding the wide variety of slip behaviors in faultings. [ABSTRACT FROM AUTHOR]