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This study pertains to the Chi-Chi earthquake of 1999 (a Richter magnitude (ML) of 7.3), the Meishan earthquake of 1906 (a Richter magnitude (ML) of 7.1) and the Hualien earthquakes of 1951 (a Richter magnitude (ML) of 7.3), which were triggered by the Chelungpu, Meishan and Milun faults. Two back-propagation neural networks (BPNNs)—(1) an embedded earthquake Richter magnitude (ML) prediction BPNN model and (2) an active probability BPNN model—are used to predict recurrence times over 500 years. Recurrence times for a 500-year period have been studied previously. This study examines the three earthquakes again and compares the results with those for previous studies. This process does not use any probability model with exceedance probability. The Chelungpu fault and the Tamaopu-Shuangtung fault are shown to more strongly couple. This viewpoint agrees with previous studies, which suggests that the Chi-Chi earthquake was caused by the Chelungpu faults in 1999. Its recurrence time with a Richter magnitude (ML) of more than 7 is 210 years after the Chi-Chi earthquake, and the highest probability is more than 60%. The Meishan earthquake is confirmed to have been caused by the Meishan fault in 1906. There is a high probability of more than 60% of another Meishan earthquake with a Richter magnitude (ML) of more than 7 in 170 years. There is a high probability of more than 60% for the occurrence of an earthquake with a Richter magnitude (ML) of more than 7 in Hualien due to the Milun faults. The results for both BNNN models are more realistic than those of previous studies because only the earthquake catalog is used, so that the cost of study is reduced.

The analysis of seismic hazards relies on the statistical analysis of historical seismic data and the instrumental seismic catalog to obtain the regional earthquake recurrence interval and earthquake probability. The accuracy of analysis thus depends strongly on the completeness of the seismic data used. However, available seismic catalogs are too short or incomplete for the reliable analysis of the statistical characteristics of earthquakes. If a long-term synthetic seismic catalog can be generated using a physics-based numerical simulation, and the simulation results match the crustal deformation, seismicity, and other observations, then such a synthetic catalog helps us to further understand the characteristics of seismic activity and analyze the regional seismic hazard. In this paper, taking the northeastern Tibetan Plateau as a case study, we establish a three-dimensional visco-elastoplastic finite-element model to simulate earthquake cycles and the spatiotemporal evolution of earthquakes on the model fault system and obtain a seismic catalog on a time scale of tens of thousands of years. On the basis that the model satisfies the regional geodynamics of the northeastern Tibetan Plateau, we analyze seismicity on the northeastern Tibetan Plateau using the simulated synthetic earthquake catalog. The characteristics of earthquake recurrence at different locations and different magnitudes, and the long-term average probability of earthquake occurrence within the fault system on the northeastern Tibetan plateau are studied. The results are a reference for regional seismic hazard assessment and provide a basis for the physics-based numerical prediction of earthquakes.

The objective of the present study is to develop a seismotectonic map and seismicity parameters for the Amaravati area, part of Peninsular India. Amaravati is the proposed capital of Andhra Pradesh, India. The seismic influence zone for the present study is considered as a circular area within a 400 km radius from the High Court of Andhra Pradesh. A total of 919 earthquake events of all ranges of magnitude are covered under a specified influence zone. An earthquake catalog containing both historical and instrumental earthquake events of a moment magnitude (MW) ≥ 3.5 from the year 1800 to 2020 is compiled from various sources. Main shocks were identified from the raw catalog and the completeness analysis was carried out. The magnitude of completeness for the present catalog data is fairly complete at the moment magnitude (MW) of 2.7. The completeness period for different classes of magnitude such as 3.5–3.99, 4.0–4.49, 4.5–4.99, 5.0–5.49, 5.5–5.99, and MW ≥ 6 is 50, 60, 60, 65, 220, and 220 years respectively. The estimated seismicity parameters a and b values for the Amaravati area are in the range of 2.70 to 3.6 and from 0.75 to 0.88, respectively. The maximum expected earthquake magnitude of Amaravati was found to be 6.7. The fault map and seismotectonic map of the Amaravati region were also developed, which are very useful for seismic hazard analyses.

Earthquake catalogs are often contaminated by man-made crustal activities such as quarry blasts. That is the case in northern Egypt, where many of cement quarries were working so long time ago since the beginning of the twentieth century (1911). Therefore, it is necessary and essential to separate these quarry blast events from the earthquakes for real seismicity and hazard analysis. Generally, discrimination of quarry blasts from tectonic events often done through different techniques and methods. In this study, the time and frequency-domain analyses of the Egyptian National Seismological Network (ENSN) digital seismograms have performed using three techniques and methods (S/P wave amplitude peak ratio, complexity, and spectral ratio). Moreover, the power of event (Pe) analysis comprising three techniques (S/P wave amplitude peak ratio, complexity, spectral ratio) was also used together to extend the discrimination accuracy as well. Finally, we have used a linear discrimination function (LDF) analysis. A total of 1473 seismic event waveforms (ML ≤ 3.0) from the ENSN digital database have been investigated. The obtained results indicate that for West of Nile Dislocation (zone no. 1) 78.1% of the investigated seismic events are tectonic events; however, 21.1% are quarry events and 0.8% are misclassified events. For the East Nile Dislocation (zone no. 2) 36.2% and 63.7% are earthquakes and quarry blast events, respectively and 0.1% are misclassified events. This means that the earthquake catalog for zone no. 2 in northern Egypt is highly contaminated and needs very high concern during the further treats especially with microearthquakes dataset for actually real seismicity and hazard analysis.

In earthquake seismology, an independent earthquake can produce a set of clusters having fore- and/or aftershocks. The main purpose of seismicity declustering is to refine a given earthquake catalog in order to retain independent events. The goal of retention of independent events by only declustering is a crucial benchmark for most of the mainshock-based analysis in seismology. In the present article, we used a re-updated unified earthquake catalog of Turkey and obtained several declustered catalogs applying different declustering methods. To compare the performance of applied declustering methods, each declustered catalog was then examined by simulation envelopes and Monte Carlo tests using some summary statistics for temporal and spatial point patterns. We found that the declustering method of Zhuang et al. (2002) based on the Epidemic Type Aftershock Sequence (ETAS) model, original version, and particularly Grunthal’s variant of the Gardner and Knopoff (1974) method seemed to be most successful in finding and removing clusters in space and time for the earthquake catalog of Turkey examined.

We analyze seismic tremor recorded during eruptive activity over the course of the 2016–2017 eruption of Bogoslof volcano, Alaska. Only regional recordings of the tremor wavefield exist for Bogoslof, making it a challenge to place the recordings in context with other eruptions that are normally captured by local seismic data. We apply a technique of time-frequency polarization analysis to three-component seismic data to reveal the wavefield composition of Bogoslof eruption tremor. We find that at regional distances, the tremor is dominated by P-waves in the band from 1.5 to 10 Hz. Using this information, along with an enriched Bogoslof earthquake catalog, we obtain estimates of average reduced displacement (DR) for eruption tremor during 25 of the 70 Bogoslof events. DR reaches as high as approximately 40 cm2 for two of the major events, similar to other VEI~3 eruptions in Alaska. Overall, average reduced displacement displays a weak correlation to plume height during the first half of the 9-month-long eruption sequence, with a few notable exceptions. The two events with the highest DR values also generated measurable eruption tremor at very-long-periods (VLP) between 0.05 and 0.15 Hz.

This research demonstrates the utilization of spatial arrangement investigation methods for earthquake series generated along Chaman Fault in Balochistan region to put an effort to identify clusters, discover local and global spatial configurations for the incident of earthquakes occurred from 1900 to 2017 with geographical information system (GIS). The preferred method in this research was global Moran’s I, Getis–Ord Gi*, quadrant count analysis, Getis–Ord general G, kernel density estimation, average nearest neighbor, Anselin Local Moran’s I and geographical coverage of the data. Each method was executed in the GIS, so that calculations could be conceded out rapidly and proficiently. Outcomes exhibited that such methods are proficient of identifying clusters in the spatial configurations of earthquakes. Both local and global spatial statistics suggested that earthquakes are populated in the northern Balochistan where the Chaman Fault bends and have higher seismicity. This study also reveals that earthquakes with higher magnitudes are particularly intense in the north Balochistan region where earthquake activities are utmost active along Chaman Fault. Lastly this study also shows that earthquakes having moderate magnitudes were predominantly rigorous in southern Balochistan because the region is formed from continental rifting giving no recognizable spreading centers of earthquakes. We conclude from this research that the pattern investigation methods applied earthquake catalog in Balochistan province along Chaman fault could spot clusters from the events of earthquakes.

The main goal of this article is to decluster Iranian plateau seismic catalog by the epidemic-type aftershock sequence (ETAS) model and compare the results with some older methods. For this purpose, Iranian plateau bounded in 24°–42°N and 43°–66°E is subdivided into three major tectonic zones: (1) North of Iran (2) Zagros (3) East of Iran. The extracted earthquake catalog had a total of 6034 earthquakes (Mw > 4) in the time span 1983–2017. The ETAS model is an accepted stochastic approach for seismic evaluation and declustering earthquake catalogs. However, this model has not yet been used to decluster the seismic catalog of Iran. Until now, traditional methods like the Gardner and Knopoff space–time window method and the Reasenberg link-based method have been used in most studies for declustering Iran earthquake catalog. Finally, the results of declustering by the ETAS model are compared with result of Gardner and Knopoff (Bull Seismol Soc Am 64(5):1363–1367, 1974), Uhrhammer (Earthq Notes 57(1):21, 1986), Gruenthal (pers. comm.) and Reasenberg (Geophys Res 90:5479–5495, 1985) declustering methods. The overall conclusion is difficult, but the results confirm the high ability of the ETAS model for declustering Iranian earthquake catalog. Use of the ETAS model is still in its early steps in Iranian seismological researches, and more parametric studies are needed.

In 1972, V. Keilis-Borok and I. Gelfand introduced the phenomenological approach based on the morphostructural zoning and pattern recognition for identification of earthquake-prone areas. This methodology identifies seismogenic nodes capable of generating strong earthquakes on the basis of geological, morphological, and geophysical data, which do not contain information on past seismicity. In the period 1972–2018, totally, 26 worldwide seismic regions have been studied and maps showing the recognized earthquake-prone areas in each region have been published. After that, 11 of these regions were hit by earthquakes of the relevant sizes. The goal of this work is to analyze the correlation of the post-publication events with seismogenic nodes defined in these 11 regions. The test was performed using the NEIC earthquake catalog because it uniformly defines the location and magnitudes of earthquakes over the globe. The ArcMap facilities were exploited to plot the post-publication events on the maps showing the recognized seismogenic nodes. We found that about 86% of such events fall in the recognized seismogenic nodes. The performed test proved the sufficient validity of the methodology for identifying areas capable of strong earthquakes and confirms the idea on nucleating strong earthquakes at the nodes.

Before the ML 6.6 Meinong earthquake in 2016, intermediate-term quiescence (Qi), foreshocks, and short-term quiescence (Qs) were extracted from a comprehensive earthquake catalog. In practice, these behaviors are thought to be the seismic indicators of an earthquake precursor, and their spatiotemporal characteristics may be associated with location, magnitude, and occurrence time of the following main shock. Hence, detailed examinations were carried out to derive the spatiotemporal characteristics of these meaningful seismic behaviors. First, the spatial range of the Qi that occurred for ~ 96 days was revealed in and around the Meinong earthquake. Second, a series of foreshocks was present for ~ 1 day, clustered at the southeastern end of the Meinong earthquake. Third, Qs was present for ~ 3 days and was pronounced after the foreshocks. Although these behaviors were recorded difficultly because the Qi was characterized by microseismicity at the lower cut-off magnitude, between ML 1.2 and 1.6, and most of the foreshocks were comprised of earthquakes with a magnitude lower than 1.8, they carried meaningful precursory indicators preceding the Meinong earthquake. These indicators provide the information of (1) the hypocenter, which was indicated by the area including the Qi, foreshocks, and Qs; (2) the magnitude, which could be associated to the spatial range of the Qi; (3) the asperity locations, which might be related to the areas of extraordinary low seismicity; and (4) a short-term warning leading of ~ 3 days, which could have been announced based on the occurrence of the Qs. Particularly, Qi also appeared before strong inland earthquakes so that Qi might be an anticipative phenomenon before a strong earthquake in Taiwan.

In this paper, the following seismic parameters, the maximum recorded magnitude ( $$M_{max})$$ , the Gutenberg–Ritcher b-value and the (normalized) mean seismic activity rate, AR, have been calculated for the Iberian Peninsula and surroundings. A geographic information system has been employed to compile all data, to work with different geographic systems and to generate the maps. An improved version of the National Geographic Institute of Spain earthquake catalog has been considered as input. Due to the detection network evolution and the extent of the territory, completeness values must be sectored to obtain reliable b-values and AR values. So, a previous work on regionalization has been considered. First, a working catalog has been elaborated. To do so, the size of some shocks through specific studies have been reviewed, magnitudes have been converted to moment magnitude ( $$M_{w})$$ and dependent events have been removed. Second, for the b-value and the AR calculation a method that considers inhomogeneous catalogs, different magnitudes and various years of completeness has been employed. Also, different decluster parameters and various minimum number of events have been considered. Finally, to represent the values, a multi-resolution grid $$(0.5^{{{\circ }}}\times 0.5^{{{\circ }}}$$ , $$1^{{{\circ }}}\times 1^{{{\circ }}}$$ and $$2^{{{\circ }}}\times 2^{{{\circ }}})$$ has been deployed. The pictures obtained show the seismicity in the terms of size, stress-meter and frequency. The highest $$M_{max}$$ has been obtained in the SW of the Iberian Peninsula with a marine epicenter. Regarding the b-value, in the contact boundary between the Africa and Eurasian plates this value is around 1.0 or minor. Contrariwise, in the mainland, values higher than 1.2 are predominant. Finally, the highest AR values are found in the SE of the Iberian Peninsula and remarkable values are also present in the NE.

To study the prospective areas of upcoming strong-to-major earthquakes, i.e., M w ≥ 6.0, a catalog of seismicity in the vicinity of the Thailand-Laos-Myanmar border region was generated and then investigated statistically. Based on the successful investigations of previous works, the seismicity rate change (Z value) technique was applied in this study. According to the completeness earthquake dataset, eight available case studies of strong-to-major earthquakes were investigated retrospectively. After iterative tests of the characteristic parameters concerning the number of earthquakes (N) and time window (T w ), the values of 50 and 1.2 years, respectively, were found to reveal an anomalous high Z-value peak (seismic quiescence) prior to the occurrence of six out of the eight major earthquake events studied. In addition, the location of the Z-value anomalies conformed fairly well to the epicenters of those earthquakes. Based on the investigation of correlation coefficient and the stochastic test of the Z values, the parameters used here (N = 50 events and T w = 1.2 years) were suitable to determine the precursory Z value and not random phenomena. The Z values of this study and the frequency-magnitude distribution b values of a previous work both highlighted the same prospective areas that might generate an upcoming major earthquake: (i) some areas in the northern part of Laos and (ii) the eastern part of Myanmar.

Probabilistic seismic hazard analysis (PSHA) generally requires the identification of line sources (active faults) and area sources where seismicity parameters must be determined. It is not easy to identify seismic sources and to estimate seismicity parameters for sources in the intraplate region. We perform an alternative PSHA with a synthetic earthquake catalog, which does not require the delineation of seismic sources. A synthetic catalog of the Korean Peninsula for 500,000 years is constructed by simulating earthquakes using the Monte Carlo method in such a way that an earthquake is randomly selected from the observed earthquake catalog, its epicenter is perturbed by a normally distributed random number, and a magnitude is assigned to the simulated event with a random value generated based on the Gutenberg-Richter magnitude-frequency relation with specified minimum and maximum magnitudes. The seismicity of the Korean Peninsula is thoroughly investigated for estimation of parameters required for synthesizing the catalog. The SMSIM computer program is used to simulate ground motions at sites instead of estimating the ground motion prediction equation. Two sites are chosen for PSHA; the one is the Seoul City Hall site (Seoul site), a densely populated metropolitan site, and the other is the Gyeongju City Hall site (Gyeongju site) close to the epicenter of the M L 5.8 earthquake on 12 September 2016. Seismic hazard curve, uniform hazard spectra (UHSs), and deaggregation of hazard for two sites are presented. The mean return periods for 0.1, 0.2, and 0.3 g at the Seoul site appears to be 1640, 6170, and 17650 years, respectively while those at the Gyeongju site appears to be 327, 1197, and 3548 years, respectively. The mean return periods for the Seoul site are around five times longer than those for the Gyeongju site, and this fact implies that the seismic hazard level of the Gyeongju site is considerably higher than that of the Seoul site. UHSs for 10% and 2% probabilities of exceedance over 50 years are constructed at both sites. The spectra show peak amplifications around the 0.05-s period.

In a study by Zare et al. (2014), a new earthquake catalog of the Middle East region has been developed consisting of historical, early, and modern instrumental events recorded between 1250 B.C. and 2006. This valuable effort was undertaken under the framework of the global earthquake model (GEM) and the earthquake model of the Middle East (EMME) projects. The final goal was to establish a unified catalog of seismicity by incorporating regional and international data to be used for homogeneous estimate of seismic hazards in the region (Erdik et al. 2012). However, observations show that magnitude of completeness (Mc) is not temporally and spatially homogeneous throughout the catalog. My goal in this commentary is to provide more insights on this important characteristic of the catalog and some suggestions on selection of homogeneous parts of the catalog. This can further aid users in using the catalog for different purposes.

Kahramanmaras and its surroundings are under the influence of East Anatolian and Dead Sea fault zones which have significance in the tectonics of Turkey. The long-term energy accumulation in these zones creates a very high risk level in terms of seismic hazard. In this study, the seismic hazard of Kahramanmaras Province and its vicinity was tried to be determined by using the probabilistic seismic hazard method approach. The earthquake catalog used in the study comprises 424 earthquakes equal or greater than M w = 4.0, covering a time period between 1 January 1900 and 1 January 2015. The earthquake data have been compiled from the catalogs of the International Seismological Center (ISC), Republic of Turkey Prime Ministry Disaster and Emergency Management Precidency (RTPMDEMP), Bogazici University Kandilli Observatory and Earthquake Research Institute. Seismic sources that could affect the study area have been identified according to the Earthquake Model of the Middle East (EMME). Seismic hazard parameters and peak horizontal acceleration values were obtained by using the selected attenuation relationships, and the results were given with iso-acceleration maps corresponding to a recurrence period of 475 years. The calculated peak horizontal acceleration values are generally varying between 0.21 and 0.41 in the study area. The result of this study shows that the southeastern parts of the study area have a greater seismic hazard compared with other parts.

We analyzed the aftershock sequence of the 2008 Wenchuan earthquake from May 12, 2008 to May 12, 2013 using the earthquake catalog of the China Earthquake Networks Center (CENC). In the analysis performed, we took under consideration the temporary variation in the completeness of the earthquake catalog just after the Wenchuan mainshock. The cutoff completeness magnitude from May 12 to June 27, 2008 was above 3.0 due to the impact of the earthquake sequence on the seismological observatory practice. It was observed that the b value has an increasing trend from June 27, 2008 to late April 2009, while since May 2009, the b value has remained stable. If these characteristics were associated with the possible signature of fault healing, the ‘apparent healing time’ could be pinpointed by this measure as around 1 year. Due to two strong asperities present on the rupture of the Wenchuan mainshock, the aftershock zone can be divided into two segments, namely the north and the south segment. The b values of the two segments seem to show different trends of temporal variation. The main contribution of the increasing trend comes from the south segment, or the ‘initiation segment’ of the main rupture.

Homogenization of earthquake catalog is the first step for calculation of seismic hazard assessment in any required region. Conversion of different calculated magnitudes types, e.g., Mb, Ms, to the unified magnitude value is the base for this homogeneity. Earthquake Monitoring Center (EMC) in Sultan Qaboos University published a regular annual bulletin including the observed regional and global events, with calculated magnitude usually deviated noticeably from the values calculated by international centers. This paper aims to calibrate the regional magnitude relations used by EMC with the global moment magnitude value to develop a regressed relation to be used to calculate magnitude for regional events precisely. Standard least square regression method usually fails to give reliable results when both regressed variables have measurement errors. We apply orthogonal standard regression as the most known reliable tool used for conversion of different magnitude values with a unified well-defined value (moment magnitude Mw in our case). Seven hundred events were picked from the EMC annual bulletin in the period 2011–2013; the magnitude for these events was calculated based on the general regional formula and compiled with the international centers (ISC, NEIC) to be regressed with the moment magnitude collected from EMSC and GCMT databases. The resulting relations have been checked with 20 events of the data and showed the advantage of using orthogonal regression methods to get relation used to homogenize Oman seismological catalog containing various magnitudes types.

Lack of data in time and location domain is a main problem in statistical seismology. Therefore, several methods have been developed to make synthetic catalogs to compensate these uncertainties. The approaches introduced in this paper try to decrease these uncertainties. A statistical tool has been determined to study the lack of data in time domain and revise a magnitude-frequency relationship in one of the very high-seismic regions in the world, northwest of Iran (44.00 to 48.00 E and 35.60 to 40.00 N). A geostatistical simulation method has also been utilized to reduce the uncertainties in the spatial domain. Variogram tool has been introduced as a spatial tool to assign a spatial regression among data in various directions. A geostatistical simulation produced a representative, synthetic catalog with 10,707 events to reduce spatial uncertainties (the number of data in the earthquake catalogs was 307 events). The synthetic database was classified by a geographical information system (GIS) based on simulated magnitudes to reveal the underlying seismicity patterns. Although some regions with high seismicity correspond to known faults, as far as seismic patterns are concerned, the new method could highlight locations of interest that have not been previously determined. It also suggests some previously unrecognized lineation and clusters in likely future strain release.

Richter-b and mmax are, in general, estimated independently. However, when the two parameters are to be estimated from an earthquake catalog by a parametric approach, they are linked through a probabilistic density function so that the estimation of one parameter requires the value of the other. To solve this problem, the effect of one parameter on the estimation of the other was investigated with simulated earthquake catalogs. The investigation revealed that the estimation of Richter-b was not sensitive to the mmax value. An accurate enough Richter-b could be estimated using the observed maximum magnitude, mmax, of the earthquake catalog. On the other hand, the estimation of mmax was quite sensitive to b. The mmax estimate increases as the b value increases. Therefore, it is recommended to estimate b first using mmax and then to estimate mmax using the b value that was just estimated. In addition, the efficiency of an iterative scheme was investigated. It turned out that the iterative scheme further improves the b estimate when using mmax. This scheme also yields an mmax estimate comparable to that obtained when using the true b value.

Two main goals are considered in this paper: (1) modification and computation of the local coefficients of the space-time windows in the well-known declustering algorithm introduced by Gardner and Knopoff (1974) and (2) checking the independence of the Iranian mainshocks obtained from applying the new modified model. First, 21 of the well-documented earthquake sequences of Iran in the time period of 1972 to 2008 with the mainshock magnitude ranged from M w = 5.4–7.1 were used to define the new local space-time windows of declustering. Generally, using these Iranian earthquake sequences led to introduce bigger space-time windows for the new model in comparison to the Gardner and Knopoff’s (1974) windows. In the next step, to control the independence of Iranian mainshocks, the events of the Iranian earthquake catalog in the time span of 1964–2010 with moment magnitude of M w = 3.5–7.4 were used. In this respect, dependent events corresponding to the seven seismotectonic zones of Iran were removed using the new modified space-time windows. After declustering, the mainshock catalog was examined by the Kolmogorov–Smirnov goodness-of-fit test, and it was found to follow a Poisson distribution in all the studied seismotectonic zones of Iran. The same test on times between successive declustered events shows that the inter-event times of all catalogs follow an exponential distribution.

During the passage of the seismic waves from the M7.3 Kumamoto, Kyushu, earthquake on April 16, 2016, a M5.7 [semiofficial value estimated by the Japan Meteorological Agency (JMA)] event occurred in the central part of Oita prefecture, approximately 80 km far away from the mainshock. Although there have been a number of reports that M 5 triggered events. In this paper, we firstly confirm that this event is a M6-class event by re-estimating the magnitude using the strong-motion records of K-NET and KiK-net, and crustal deformation data at the Yufuin station observed by the Geospatial Information Authority of Japan. Next, by investigating the aftershocks of 45 mainshocks which occurred over the past 20 years based on the JMA earthquake catalog (JMAEC), we found that the delay time of the 2016 M5.7 event in Oita was the shortest. Therefore, the M5.7 event could be regarded as an exceptional M > 5 event that was triggered by passing seismic waves, unlike the usual triggered events and aftershocks. Moreover, a search of the JMAEC shows that in the 2016 Oita aftershock area, swarm earthquake activity was low over the past 30 years compared with neighboring areas. We also found that in the past, probably or possibly triggered events frequently occurred in the 2016 Oita aftershock area. The Oita area readily responds to remote triggering because of high geothermal activity and young volcanism in the area. The M5.7 Oita event was triggered by passing seismic waves, probably because large dynamic stress change was generated by the mainshock at a short distance and because the Oita area was already loaded to a critical stress state without a recent energy release as suggested by the past low swarm activity.

Along with most of the northern Pakistan and the Kashmir regions (Kashmir and eastern districts of Khyber Pakhtunkhwa), Muzaffarabad and Balakot were shaken by a predominantly disastrous earthquake of magnitude Mw 7.6 in 2005. The earthquake is expected to have killed over 80,000 people and 70,000 injured, nevertheless little recognized about its aftershocks. We studied the instrumental earthquake data from the International Seismological Centre (ISC) and United Sates Geological Survey (USGS)/Preliminary Determination of Epicenters (PDE) for the period of October 2005 to March 2006. Reasenberg’s algorithm (Reasenberg in Geophys Res 90:5479-5495, 1985) was applied to identify the aftershocks from the main earthquake catalog, and a catalog of 497 aftershock sequences is assembled during the time period of October, 08 2005 to March 20, 2006. In order to explain the variation of aftershocks, several histograms of time, magnitude, depth, and hour of the day have been made. The results show that prominent variation exists within the 3 days after a main shock of Kashmir 2005 earthquake. The size distribution of aftershocks is analyzed using the Gutenberg-Richter law, and the value of b is 1.1 ± 0.07. Omori-Utsu law was used to describe the decay rates of aftershock sequences in and around Kashmir. The decay component, p, which is generally known as “p value” is calculated to be 1.58 ± 0.07.

In recent years, a large number of quarry blasts have been detonated in the eastern Black Sea region. When these blasts are recorded by seismic stations, they contaminate the regional earthquake catalog. It is necessary to discriminate quarry blast records from the earthquake catalogs in order to determine the real seismicity of the region. Earthquakes and quarry blasts can be separated through different methods. These methods should be applied concurrently in order to safely distinguish these events. In this study, we discriminated quarry blasts from earthquakes in the eastern Black Sea region of Turkey. We used 186 seismic events recorded by the Karadeniz Technical University and Bogazici University Kandilli Observatory Earthquake Research Institute stations which are Trabzon, Espiye, Pazar, Borcka, Aydintepe, and Gumushane between years of 2002 and 2010. For the discrimination of quarry blasts from earthquakes, we used both, statistical methods (calculation of the maximum ratio of S to P waves (S/P), complexity (C)) and spectral methods (spectrogram calculation). These methods included measuring the maximum amplitude S/P, C, spectral ratio, and time-frequency analysis. We especially relied on two-dimensional time-frequency analysis methods to discriminate quarry blasts from earthquakes in Turkey. As a result of this study, 68 % of the examined seismic events were determined to be quarry blasts and 32 % to be earthquakes. The earthquakes occurring on land are related to small faults and the blasts are concentrated in large quarries. Nearly 40 % of the earthquakes occurred in the Black Sea, most of them are related to the Black Sea thrust belt, where the largest earthquake was observed in the time period studied. The areas with the largest earthquake potential in the eastern Black Sea region are in the sea.

This study first presents the series of peak ground acceleration (PGA) in the three major cities in Taiwan. The PGAs are back-calculated from an earthquake catalog with the use of ground motion models. The maximums of the 84th percentile (mean + one standard deviation) PGA since 1900 are 1.03, 0.36, and 0.10 g, in Taipei, Taichung, and Kaohsiung, respectively. Statistical goodness-of-fit testing shows that the series of PGA follow a double-lognormal distribution. Using the verified probability distribution, a probabilistic analysis was developed in this paper, and used to evaluate probability-based seismic hazard. Accordingly, given a PGA equal to 0.5 g, the annual exceedance probabilities are 0.56, 0.46, and 0.23 % in Taipei, Taichung, and Kaohsiung, respectively; for PGA equal to 1.0 g, the probabilities become 0.18, 0.14, and 0.09 %. As a result, this analysis indicates the city in South Taiwan is associated with relatively lower seismic hazard, compared with those in Central and North Taiwan.

In this paper, an artificial neural network (ANN)–based methodology is proposed to determine the probability of inter-arrival time (IAT) of main shock of six broad seismic regions of India. Initially, classical methodology using exponential distribution is applied to IAT of earthquake events computed from earthquake catalog data. From the goodness-of-fit test results, it has been found that exponential distribution is not adequate. In this paper, a more efficient ANN-based methodology is proposed, and two ANN models are developed to determine the probability of IAT of earthquake events for a specified region, specified magnitude range or magnitude greater than the specified value. The performance of ANN models developed is validated with number of examples and found to predict the probability with minimal error compared to exponential distribution model. The methodology developed can be applied to any other region with the database of the respective regions.

A catalog for northeast India and the adjoining region for the period 1897–2009 with 4,497 earthquakes events is compiled for homogenization to moment magnitude M w,GCMT in the magnitude range 3–8.7. Relations for conversion of m b and M s magnitudes to M w,GCMT are derived using three different methods, namely, linear standard regression, inverted standard regression (ISR) and orthogonal standard regression (OSR), for different magnitude ranges based on events data for the catalog period 1976–2006. The OSR relations for M s to M w,GCMT conversion derived in this paper have significantly lower errors in regression parameters compared to the relations reported in other studies. Since the number of events with magnitude ≥7 for this region is scanty, we, therefore, considered whole India region to obtain the regression relationships between M w,GCMT and M s,ISC. A relationship between M w,GCMT and M w,NEIC is also obtained based on 17 events for the range 5.2 ≤ magnitude ≤ 6.6. A unified homogeneous catalog prepared using the conversion relations derived in this paper can serve as a reference catalog for seismic hazard assessment studies in northeast India and the adjoining region.

This investigation covers the area bounded by latitudes 20° to 33° N and longitudes 9.5° to 25°E.The seismicity of area for the period 1900–2005 is evaluated. Libyan earthquake catalog is complete for the 4.4 M and greater over a 70-year span. The overall seismicity of Libya is found to be low to intermediate. The seismic activity is concentrated in three zones of the northern Libya. Outside of these zones, epicenters are scattered and sparsely distributed. The b value for Libya is –0.71. This low b value is a characteristic feature for intraplate environment. A seismotectonics map is constructed for Libya. It shows that the epicenters agree well with the distribution of the major tectonic features. Majority of seismic activity in Libya is concentrated near Hun Graben and Cyrenaica, and the locations of earthquakes are near the transition zones between the stress domains in northern Libya. These transition zones are locations of stress concentration. This investigation suggests that the stress concentration theory is generally considered as causative mechanism for seismicity of Libya.

Two great earthquakes of MS8.5 and MS8.3 determined by the China Earthquake Networks Center (CENC) occurred successively on September 12 and 13, 2007 in the sea area to the south of Sumatra, which is another group of large earthquakes after MS8.7 event on December 26, 2004 and MS8.5 event on March 29, 2005. The magnitudes of these earthquakes determined by the National Earthquake Information Center of USA (NEIC) are MW9.0 (26 December 2004), MW8.7 (29 March 2005), MW8.4 (12 September 2007) and MW8.1 (13 September 2007), respectively. Many researches about the two earthquakes of 2004 and 2005 have been developed (Chlieh et al, 2007; Ammon et al, 2005; ZHANG et al, 2005). XUE et al (2005a) studied the characteristics of seismic activity before the MW9.0 and make comparison between the two great earthquake sequences of 2004 and 2005 (XUE et al, 2005b). When analyzing spatial distribution of the two sequences, XUE et al (2005a) found a seismic gap with 400 km long and thought the seismic gap maybe a potential strong earthquake region taking historical earthquake activity there into account. It is interesting that the two earthquakes of 2007 just occurred in the seismic gap. Moreover the abnormal phenomena of the global and regional seismicity before the two earthquakes are similar to those before the large earthquake of 2004. In this paper, we will contrastively analyze the characteristics of seismic activity before the four large earthquakes and try to find the common features. The data used in this paper are from global earthquake catalog given by NEIC and the global earthquake catalog with MS≥7.0 obtained by CENC respectively. The earthquake catalog of NEIC can also cover earthquakes with M≥4.8 in Sumatra and its neighboring region (XUE et al, 2005a).

It is observed that the parameter of seismic inhomogeneous degree (GL value) calculated from the earthquake catalog shows obvious abnormal changes prior to strong earthquakes, indicating the state change of local seismic activity. This paper focuses on the mechanism for the abnormal changes of the GL values based on the sequences of acoustic emission for three types of rock samples containing macro-asperity fracture; compressional en-echelon fracture and model-III shear fracture. The results show that for the three types of rock samples, there are continuous abnormal changes of GL value (>1) just before the non-elastic deformation occurs or during the process of nucleation prior to the instability. Based on the experimental results, it seems that the process of creep sliding and resistance-uniformization along fault zone is the possible mechanism for the abnormal changes of GL value before rock fractures.

The earthquake on December 9, 1755 is one of the major events in the Valais region, having an important influence on the seismic hazard assessment of the area. The re-evaluation of the event was undertaken in the course of upgrading the Earthquake Catalog of Switzerland (ECOS). It is now based on a newly investigated and reliable database created through research in archives and libraries. Using the data made available by the historical information, we assigned site intensities according to the criteria established by the European macroseismic scale EMS 98 (Grunthal 1998). Based on the broad spectrum of the available information, we assigned minimum and maximum possible values (Imin; Imax) and determined a most probable intensity value (Iw) for each site. The maximum observed intensity, Ix, is the largest intensity for each quake. Epicentral intensity, I0, is equal to the maximum observed intensity Ix, if at least two data points are assigned an intensity of Ix. We obtained maximum Ix = I0 = VIII at Brig/VS (46.3/8.0) and moment magnitude Mw = 6.1.

The location of the September 3, 1295 earthquake has so far been assumed to be in the Central Alps. It was assessed at an intensity VIII in the catalogue MECOS 99 in MSK. This event was recently analyzed within the “Revision of the Earthquake Catalog of Switzerland” (ECOS), a project carried out by the Institute of Geophysics at the Swiss Federal Institute of Technology Zurich (ETHZ) from 2000–2002. Additional sources and newly interpreted information regarding observers, copies, place names and dating have now made it possible to more precisely locate the event at Churwalden and analyze its effects in more detail. The assessment of the intensity of VIII having been confirmed, this event is classified as one of the seven strongest quakes of the last millennium known in Switzerland.

Upgrading the Earthquake Catalog of Switzerland (ECOS) included revising the earthquake of 1720. This change has major importance for history and seismology.Although that quake has been the subject of several publications, none was based on critical methods. This re-evaluation of the event is built upon a new and more reliable database established after investigating archives and libraries. Using data from such historical sources, we assigned new site intensities, adopting the criteria established by the European macroseismic scale EMS 98 (Grunthal, 1998).We discovered that the event had been assigned an overestimated intensity, due to interpretation errors in former earthquake catalogs and compilations. We recommend reducing the intensity from I0= VIII to I0= VI (EMS 98). The moment magnitude is given as MW= 4.6. Since the event had been considered the largest for its respective area, downgrading it now will influence the seismic hazard assessment for this region.

Firstly, the impact of historical earthquakes on 34 China province-level capital cities is evaluated by using historical earthquake catalog. The distribution of affected intensity shows, about 53% of cities have even not been affected by earthquake intensity VI, and 44% of cities have been hit by earthquake intensity VII to IX. For most of the cities, occurrence frequency of affected intensity VI is usually higher than that of affected intensity larger than VI, and the value of affected intensity with maximal occurrence frequency may be very different among cities. So both the maximal affected intensity and the affected intensity with maximal occurrence frequency should be taken into account when the prevention seismic intensity needs to be determined. Secondly, considering the incompleteness of records of historical earthquakes, a method of earthquake catalog computer simulation is introduced to study the features of affected intensity of big cities. 69 county-level cities of Fujian Province are selected to be statistical objects. The statistical result shows, for different risk levels the seismic intensity changes greatly among cities, the seismic intensity of 2% probability of exceedance in 50 years can be regarded as the characteristic affected intensity of city, and can be the basis of determining the city special earthquake prevention level and a proper indicator of future earthquake’s impact on cities.

A systematic test on seismic quiescence occurring before largeearthquakes is conducted. For a fixed geographical location, the degree ofclustering in space and time is analysed and the results are testedagainst randomized earthquake catalogs.A gridding technique allows to investigate the entirespatial volume covered by a certain earthquake catalog. The result is a significance K(x,t) for seismic quiescence as a function ofspace and time. A point (x,t) is considered as quiet, if K(x,t) exceeds a threshold value K(99) such that the nullhypothesis is rejected with a probability of p≥ 99%. Becauseearthquake clusters, like aftershocks and swarm events, generateerroneous quiescence, declustered catalogs are also investigated andthe influence of the clusters is discussed.Applying this method to an earthquake catalog from Armenia,several cases of seismic quiescence before mainshocks are obtained.These quiescence periods occur in the originaldata as well as in the declustered data. Using alarm conditions, itis found that quiescence periods and mainshocks are correlated`better-than-chance'. Thus, the results support the claim thatseismic quiescence makes a contribution to the improvement of seismichazard assessment.

Based on a cellular automata model, which obeys rules produced by a spring-damper-slider model of fault network, a synthetic earthquake catalog of deterministic chaos can be produced. It is a challenge to inverse the model parameters and predict the synthetic earthquakes from the synthetic catalog. We apply an improved statistical model of coupled stress release to the synthetic catalog, it does successfully inverse the stress evolution of the system, but effectively prediction of the earthquakes from the stresses remains a problem.