An evaluation of earthquake hazard parameters in the Iranian Plateau based on the Gumbel III distribution

The Gumbel’s third asymptotic distribution (GIII) of the extreme value method is employed to evaluate the earthquake hazard parameters in the Iranian Plateau. This research quantifies spatial mapping of earthquake hazard parameters like annual and 100-year mode beside their 90 % probability of not being exceeded (NBE) in the Iranian Plateau. Therefore, we used a homogeneous and complete earthquake catalogue during the period 1900–2013 with magnitude M _w ? ≥?4.0, and the Iranian Plateau is separated into equal area mesh of 1° late?×?1° long. The estimated result of annual mode with 90 % probability of NBE is expected to exceed the values of M _w 6.0 in the Eastern part of Makran, most parts of Central and East Iran, Kopeh Dagh, Alborz, Azerbaijan, and SE Zagros. The 100-year mode with 90 % probability of NBE is expected to overpass the value of M _w 7.0 in the Eastern part of Makran, Central and East Iran, Alborz, Kopeh Dagh, and Azerbaijan. The spatial distribution of 100-year mode with 90 % probability of NBE uncovers the high values of earthquake hazard parameters which are frequently connected with the main tectonic regimes of the studied area. It appears that there is a close communication among the seismicity and the tectonics of the region.     

Earthquakes Along the Passive Margin of Greenland: Evidence for Postglacial Rebound Control

—?An intriguing observation in Greenland is a clear spatial correlation between seismicity and deglaciated areas along passive continental margins, a piece of evidence for earthquake triggering due to postglacial rebound. Another piece of evidence for induced seismicity due to deglaciation derives from earthquake source mechanisms. Sparse, low magnitude seismicity has made it difficult to determine focal mechanisms from Greenland earthquakes. On the basis of two normal faulting events along deglaciated margins and from the spatial distribution of epicenters, earlier investigators suggested that the earthquakes of Greenland are due to postglacial rebound. This interpretation is tested here by using more recent data. Broadband waveforms of teleseismic P waves from the August 10, 1993 (m _b = 5.4) and October 14, 1998 (m _b = 5.1) earthquakes have been inverted for moment tensors and source parameters. Both mechanisms indicate normal faulting with small strike-slip components: the 1993 event, strike = 348.9°, dip = 41.0°, rake =?56.3°, focal depth = 11?km, seismic moment = 1.03?×?10²⁴ dyne-cm, and M _w = 5.3; the 1998 event, strike = 61.6°, dip = 58.0°, rake =?95.5°, focal depth = 5?km, seismic moment = 5.72?×?10²³ dyne-cm, and M _w = 5.1. These and the two prior events support the theory that the shallow part of the lithosphere beneath the deglaciated margins is under horizontal extension. The observed stress field can be explained as flexural stresses due to removal of ice loads and surface loads by glacial erosion. These local extensional stresses are further enhanced by the spreading stress of continental crust and reactivate preexisting faults. Earthquake characteristics observed from Greenland suggest that the dominant seismogenic stresses are from postglacial rebound and spreading of the continental lithosphere.     

Properties of the Aftershock Sequences of the 2003 Bingöl, M D = 6.4, (Turkey) Earthquake

Aftershock sequences of the magnitude M _{W =}6.4 Bingöl earthquake of 1 May, 2003 (Turkey) are studied to analyze the spatial and temporal variability of seismicity parameters of the b value of the frequency-magnitude distribution and the p value describing the temporal decay rate of aftershocks. The catalog taken from the KOERI contains 516 events and one month’s time interval. The b value is found as 1.49 ± 0.07 with Mc =3.2. Considering the error limits, b value is very close to the maximum b value stated in the literature. This larger value may be caused by the paucity of the larger aftershocks with magnitude M _D ≥ 5.0. Also, the aftershock area is divided into four parts in order to detect the differences in b value and the changes illustrate the heterogeneity of the aftershock region. The p value is calculated as 0.86 ± 0.11, relatively small. This small p value may be a result of the slow decay rate of the aftershock activity and the small number of aftershocks. For the fitting of a suitable model and estimation of correct values of decay parameters, the sequence is also modeled as a background seismicty rate model. Constant background activity does not appear to be important during the first month of the Bingöl aftershock sequences and this result is coherent with an average estimation of pre-existing seismicity. The results show that usage of simple modified Omori law is reasonable for the analysis. The spatial variability in b value is between 1.2 and 1.8 and p value varies from 0.6 to 1.2. Although the physical interpretation of the spatial variability of these seismicity parameters is not straightforward, the variation of b and p values can be related to the stress and slip distribution after the mainshock, respectively. The lower b values are observed in the high stress regions and to a certain extent, the largest b values are related to Holocene alluvium. The larger p values are found in some part of the aftershock area although no slip occurred after the main shock and it is interpreted that this situation may be caused by the alluvium structure of the region. These results indicate that the spatial distribution in b and p values are generally related to the rupture mechanism and material properties of an aftershock area.     

An investigation of seismicity for the Central Anatolia region,Turkey

The aim of this study is to investigate the seismicity of Central Anatolia, within the area restricted to coordinates 30–35° longitude and 38–41° latitude, by determining the “a” and “b” parameters in a Gutenberg–Richter magnitude–frequency relationship using data from earthquakes of moment magnitude (Mw)?≥?4.0 that occurred between 1900 and 2010. Based on these parameters and a Poisson model, we aim to predict the probability of other earthquakes of different magnitudes and return periods (recurrence intervals). To achieve this, the study area is divided into six seismogenic zones, using spatial distributions of earthquakes greater than Mw?≥?4.0 with active faults. For each seismogenic zone, the a and b parameters in the Gutenberg–Richter magnitude–frequency relationship were calculated by the least squares method. The probability of occurrence and return periods of various magnitude earthquakes were calculated from these statistics using the Poisson method.     

Interrelation between seismicity parameters and delimiting potential seismic sources in a seismic statistical region and its influence on seismic risk estimation

In the paper, we have discovered the abnormal area distribution features of maximum variation values of ground motion parameter uncertainty with different probabilities of exceedance in 50 years within the range of 100°～120°E,29°～42°N for the purpose to solve the problem that abnormal areas of maximum variation values of ground motion parameter uncertainties emerge in a certain cities and towns caused by seismicity parameter uncertainty in a seismic statistical region in an inhomogeneous distribution model that considers tempo-spatial nonuniformity of seismic activity. And we have also approached the interrelation between the risk estimation uncertainty of a site caused by seismicity parameter uncertainty in a seismic statistical region and the delimitation of potential sources, as well as the reasons for forming abnormal areas. The results from the research indicate that the seismicity parameter uncertainty has unequal influence on the uncertainty of risk estimation at each site in a statistical region in the inhomogeneous distribution model, which relates to the scheme for delimiting potential sources. Abnormal areas of maximum variation values of ground motion parameter uncertainty often emerge in the potential sources of Mu≥8 (Mu is upper limit of a potential source) and their vicinity. However, this kind of influence is equal in the homogeneous distribution model. The uncertainty of risk estimation of each site depends on its seat. Generally speaking, the sites located in the middle part of a statistical region are only related to the seismicity parameter uncertainty of the region, while the sites situated in or near the juncture of two or three statistical regions might be subject to the synthetic influences of seismicity parameter uncertainties of several statistical regions.     

Spatial Distribution of Time-independent Seismicity in China

—The seismicity in the territory of China, a seismotectonically complicated region, has been examined by using three complete samples of earthquakes which occurred during the last two centuries (1800–1995). The b value of the Gutenberg-Richter relation was estimated by using this data sample. Taking into account the fact that the b value is spatially more stable than the a value, the b values were calculated at the nodes of a normal grid superposing on the entire area studied, and their distribution was examined. The results showed that the b value increases smoothly from 0.4 in inner-Mongolia to 0.8 in the east, south and southwest of China with higher values (b>0.8) in the Taiwan region. Furthermore, keeping fixed the obtained b values, the a value distribution was also examined. In order to display more detailed information about the seismicity, smaller cell surface (10,000 km²) for the calculation of the a values was chosen. The mean return periods for different cutoff magnitudes were also calculated for each of these small cells. It was observed that the mean return periods are the shortest ones in China, which are 10 and 50 years for the magnitude larger than or equal to 6.0 and 7.0, respectively.     

Regional Variations of the <Emphasis Type="Italic">ω</Emphasis>-upper Bound Magnitude of GIII Distribution in the Iranian Plateau

The Iranian Plateau does not appear to be a single crustal block, but an assemblage of zones comprising the Alborz—Azerbaijan, Zagros, Kopeh—Dagh, Makran, and Central and East Iran. The Gumbel’s III asymptotic distribution method (GIII) and maximum magnitude expected by Kijko—Sellevoll method is applied in order to check the potentiality of the each seismogenic zone in the Iranian Plateau for the future occurrence of maximum magnitude (M_max). For this purpose, a homogeneous and complete seismicity database of the instrumental period during 1900–2012 is used in 29 seismogenic zones of the examined region. The spatial mapping of hazard parameters (upper bound magnitude (ω), most probable earthquake magnitude in next 100 years (M₁₀₀) and maximum magnitude expected by maximum magnitude estimated by Kijko—Sellevoll method (max M_{K ? S}^max) reveals that Central and East Iran, Alborz and Azerbaijan, Kopeh—Dagh and SE Zagros are a dangerous place for the next occurrence of a large earthquake.     

Deep-seated faults and lineaments, and the location of earthquake epicenters in the Russian northeast on land

This paper summarizes the available geological and geophysical material for faults as regards their role in the seismic process. The entirety of the geological and geophysical evidence is used to reveal hidden faults, which are important in influencing the spatial distribution of earthquakes, and to produce a map of the major earthquake-generating faults and lineaments in the Russian northeast. As well as the occurrence of earthquakes at known faults that have surface expression, we find that seismicity tends to occur at the hidden faults and lineaments we have identified, as well as at intersections of faults. We made a quantitative assessment of the relationship of seismicity to tectonic fragmentation of the crust, correlating the density and discordance measure for faults to indicators of seismic activity (rate and energy release of earthquakes per unit area) for the southeast flank of the Okhotsk-Lena seismic region. The results obtained in this study revealed some features in the spatial distribution of earthquakes occurring on land in the Okhotsk-Lena seismic region: the maximum level of seismic activity occurs in areas with moderate values of the discordance measure for faults (12 < ‖D‖ ≤ 18) as identified from gravity data and in zones of increased horizontal gradients of the lines of equal discordance. At these locations, the greatest probability of earthquake occurrence for events of energy class K ≥ 12 corresponds to moderate values of the density of faults visible at the surface (0.12 < τ ≤ 0.16 km^?1).     

Study of seismicity in the NW Himalaya and adjoining regions using IMS network

The Reviewed Event Bulletin (REB) of the International Data Center (IDC) has been used in order to investigate the seismicity of the Northwest Himalaya and its neighboring region for the time period June 1999 to March 2015 within the geographical coordinates 25–40° N latitude and 65–85° E longitude. We have used a very precisely located earthquake dataset recorded by the International Monitoring System (IMS) Network containing 7,583 events with body wave magnitudes from 2.5 to 6.3. The study area has been subdivided into six regions based on the Flinn-Engdahl (F-E) seismic and geographical regionalization scheme, which was used as the region classifications of the International Data Center catalog. The examined region includes NW India, Pakistan, Nepal, Xizang, Kashmir, and Hindukush. For each region, Magnitudes of completeness (Mc) and Gutenberg-Richter (GR) recurrence parameters (a and b values) have been estimated. The Gutenberg-Richter analysis is preceded by an overview of the seismotectonics of the study area. The obtained Mc values vary from 3.5 to 3.9. The lower value of Mc was found mainly in Xizang region whereas the higher Mc threshold is evident in Pakistan region. However, the b values vary from 1.19 to 1.48. The lowest b value is recorded in Xizang region, which is mostly related to the Main Karakoram Thrust (MKT) fault, whereas the highest b values are recorded in NW India and Kashmir regions, which are mostly related to the Main Frontal Thrust (MFT) fault. The REB for the selected period has been compared to the most renowned bulletin of global seismicity, namely that issued by the National Earthquake Information Center (NEIC) of the United States Geological Survey (USGS). A study of 4,821 events recorded by USGS in the study region indicates that about 36 % of seismic events were missed and the catalog is considered as complete for events with magnitudes ≥4.0. However, both a and b values are obviously higher than those of IMS catalog. The a and b parameters in the Gutenberg-Richter magnitude–frequency relationship have been utilized to forecast the probability of future earthquakes of different magnitudes and returned periods (recurrence intervals).     

Contemporary horizontal movements and seismicity of the south Baikal Basin (Baikal rift system)

The contemporary horizontal movements and deformations in the central and southern parts of the Baikal depression are analyzed, and their relationship with contemporary seismicity is studied. Based on the long-term measurements by the Baikal geodynamical GPS monitoring network, the refined estimate is obtained for the velocity of the divergence of the Siberian and Transbaikalian blocks, which is found to occur in the southeastward direction (130°) at 3.4 ± 0.7 mm per annum. This agrees with the parameters of the long-term extension component estimated from the geological data and with the direction of extension determined from the seismic data. The distribution of the displacement velocity across the strike of the rift, which gradually increases from one block to another, suggests a nonrigid behavior of the continental lithospheric plates at the divergent boundary. About 30% (1.0–1.5 mm per annum) of the total increase in the velocity is accommodated by the Baikal Basin. The strain rate within the trough reaches 3.1 × 10^?8 yr^?1 and decreases on either side across the structure. The character of distribution of the horizontal displacement velocities on the Baikal divergent boundary between the Eurasian and Amurian plates favors the model of passive rifting. The zones of highly contrasting topography and increased seismicity are localized within the area of contemporary deformations, and the seismic moment release rate directly depends on the strain rate. Here, the rate of the seismic moment release rate makes up a few percent of the geodetic moment accumulation rate calculated by the approach suggested by Anderson (1979). Based on the coherence between the graphs of the rates of geodetic moment accumulation and seismic moment release rate by the earthquakes with M ≥ 5.0 during the historical and instrumental observation periods, the contemporary seismic hazard for the South Baikal Basin could be assessed at a level of seismic event with M = 7.5–7.6.     

K-means cluster analysis and seismicity partitioning for Pakistan

Pakistan and the western Himalaya is a region of high seismic activity located at the triple junction between the Arabian, Eurasian and Indian plates. Four devastating earthquakes have resulted in significant numbers of fatalities in Pakistan and the surrounding region in the past century (Quetta, 1935; Makran, 1945; Pattan, 1974 and the recent 2005 Kashmir earthquake). It is therefore necessary to develop an understanding of the spatial distribution of seismicity and the potential seismogenic sources across the region. This forms an important basis for the calculation of seismic hazard; a crucial input in seismic design codes needed to begin to effectively mitigate the high earthquake risk in Pakistan. The development of seismogenic source zones for seismic hazard analysis is driven by both geological and seismotectonic inputs. Despite the many developments in seismic hazard in recent decades, the manner in which seismotectonic information feeds the definition of the seismic source can, in many parts of the world including Pakistan and the surrounding regions, remain a subjective process driven primarily by expert judgment. Whilst much research is ongoing to map and characterise active faults in Pakistan, knowledge of the seismogenic properties of the active faults is still incomplete in much of the region. Consequently, seismicity, both historical and instrumental, remains a primary guide to the seismogenic sources of Pakistan. This study utilises a cluster analysis approach for the purposes of identifying spatial differences in seismicity, which can be utilised to form a basis for delineating seismogenic source regions. An effort is made to examine seismicity partitioning for Pakistan with respect to earthquake database, seismic cluster analysis and seismic partitions in a seismic hazard context. A magnitude homogenous earthquake catalogue has been compiled using various available earthquake data. The earthquake catalogue covers a time span from 1930 to 2007 and an area from 23.00° to 39.00°N and 59.00° to 80.00°E. A threshold magnitude of 5.2 is considered for K-means cluster analysis. The current study uses the traditional metrics of cluster quality, in addition to a seismic hazard contextual metric to attempt to constrain the preferred number of clusters found in the data. The spatial distribution of earthquakes from the catalogue was used to define the seismic clusters for Pakistan, which can be used further in the process of defining seismogenic sources and corresponding earthquake recurrence models for estimates of seismic hazard and risk in Pakistan. Consideration of the different approaches to cluster validation in a seismic hazard context suggests that Pakistan may be divided into K?=?19 seismic clusters, including some portions of the neighbouring countries of Afghanistan, Tajikistan and India.     

A Non-Extensive Statistical Physics View in the Spatiotemporal Properties of the 2003 (Mw6.2) Lefkada,Ionian Island Greece,Aftershock Sequence

Investigation of the spatiotemporal properties of the 2003 Lefkada seismic sequence is performed through non-extensive statistical physics. Information on highly accurate aftershock source parameters became feasible from the recordings of a portable digital seismological network that was installed and operated in the study area, during the evolution of the seismic sequence. Thus, the spatiotemporal distribution of aftershocks onto the main and neighboring fault segments was investigated in detail, enabling the recognition of four distinctive seismicity clusters separated by less active patches. The aftershock spatiotemporal properties are studied here, using the ideas of non-extensive statistical physics (NESP). The cumulative distribution functions of the inter-event times and the inter-event distances are presented using the data set in each seismicity cluster, and the analysis results in values for the statistical thermodynamic q _T and q _D parameters for each cluster, where q _T varies from 1.16 to 1.47 and q _D from 0.42 to 0.77 for the inter-event times and distances distributions, respectively. These values confirm the complexity and non-additivity of the spatiotemporal evolution of seismicity, and the applicability of the NESP approach in investigating aftershocks sequence. The temporal pattern is discussed using the closely connected to NESP approach of superstatistics, which is based on a superposition of ordinary local equilibrium statistical mechanics. The result indicates that the temporal evolution of the Lefkada aftershock sequence in clusters A, B and C is governed by very low number of degrees of freedom, while D is a less organized seismicity structure with a much higher number of degrees of freedom.     

Earthquake Hazard Parameters in Crete Island and its Surrounding Area Inferred from Bayes Statistics: An Integration of Morphology of the Seismically Active Structures and Seismological Data

-- The study addresses the evaluation of earthquake hazard parameters such as maximum regional magnitude (M_max) and the slope of Gutenberg-Richter law # (where b=# log e) for the Hellenic Wadati-Benioff zone and the overriding lithospheric plate in the area of Crete and its surroundings. The seismicity of the area is divided in a cellular (1.0° 2 1.0°) manner allowing analysis of the localized earthquake hazard parameters and graphical representation of their spatial variation. Our approach incorporates the recently updated earthquake catalogue for Greece and the adjacent areas, the consideration of the morphology of the deep seismically active structures in the studied area and use of a probabilistic procedure for estimating the earthquake hazard parameters.¶One of the main inconsistencies in the earthquake hazard assessment is the estimation of the maximum magnitude and the related uncertaint y. The Bayesian approach, applied in the present, is a straightforward technique for evaluating the earthquake hazard parameters and is based on the following assumptions: Poissonian character of seismic events flow, a frequency-magnitude law of Gutenberg-Richter's type with cutoff maximal value for estimated parameter and a seismic catalogue, having a rather sizeable number of events (i.e., 50 events at least per cell). For five cells in which the number of events is less than 50, an effort is made to produce synthetic data. The re-assessed parameters obtained from the synthetic data show no significant difference and the real data (of the five cells) are finally taken into account although the estimated uncertainty is high.¶For four random cells we constructed hazard curves showing the probabilities that a certain magnitude M will be exceeded in one year and the return periods (in years) that are expected for a given magnitude. These are particularly useful for the mapping of earthquake hazard in regions of either low or high seismic activity, as is Crete and the adjacent area.¶The obtained results show that the W and E parts of both subducting and overriding plates differ in the spatial distribution of all the estimated earthquake hazard parameters. The M_max distribution indicates strong coupling between the western portions of the interacting plates (M_max > 6.3) to the south of 36°N. The smaller values of M_max (M_max < 6.3) estimated in the SE part of the studied area indicate weak coupling between the eastern portions of the subducting and overriding plates.¶Values of b > 1.0 are found to the south and east of Crete for the Wadati-Benioff zone, and over the central part of the island and the area to the northeast of it (cell 11) for the continental wedge, which suggests nonuniform stress field and/or heterogeneous material.     

A new model for seismicity parameterization and predictive aspects of its application to the Sakhalin region

Seismicity is generally treated as an example of self-organized criticality. One alternative to this treatment may possibly be furnished by a model of seismicity that is thought of as a set of episodes of avalanching relaxation that occur randomly on a set of metastable subsystems. This model is defined by the parameter r, which specifies the hierarchical divisibility of the block structure of the medium, and by the parameter p, which specifies the probability for the incipient relaxation of a metastable state to continue. These two parameters together define the modeled value of the slope of the recurrence curve, or b-value, thus determining the mode of seismicity occurrence. This model is used to describe the seismicity in southern Sakhalin Island. In this modeling, the coefficient of hierarchical divisibility r in the block structure of the medium was assumed to be stationary and the disequilibrium parameter p was assumed to describe time-dependent variations of seismicity. We calculated models for the spatial variability of r and the time variability of p. We found abnormal growth in p during the Gornozavodsk earthquake (2006, M _w = 5.6) and the Nevel??sk earthquake (2007, M _w = 6.2). At present, we report values of p that are high (and increasing over time) in the wide area of the Poyasok isthmus. The results derived here are compared with other ideas on seismicity and with the experience that was previously gained in the area of earthquake prediction.     

Focal mechanism and seismogenic structure of the Shiqu MS4.4 earthquake

The focal mechanism solution of the Shiqu M_S 4.4 earthquake occurred on May 16^th, 2017 in Sichuan Province is studied by the gCAP method using the waveform data from the regional seismic networks in Sichuan, Qinghai, Tibet and Gansu provinces. The strike/dip/dipping angle of the first nodal plane are 214°/80°/167° and those of the second nodal plane are 306°/77°/10°, the optimal centroid depth is 7.3 ​± ​0.6 ​km and the moment magnitude is M_W 4.5. Furthermore, the study investigates the robustness of the results against the error of crustal velocity structure, location, data quality and difference of seismic parameters, subsequently obtaining a stable resolved focal mechanism. According to the geological structure in the seismogenic area, spatial distribution of aftershock sequenceof the regional tectonic stress field, and the focal mechanism of the main shock, we suggest that the Shiqu earthquake is induced by a left-lateral strike-slip mechanism and the second nodal plane is inferred to be the seismogenic fault, consistent with the geometry of the Changshagongma fault which is the secondary fault of the northwest part of the Xianshuihe fault zone.     

The precursory phenomena before the Karymskii seismovolcanic crisis in parameters of seismicity in a wide range of energy

We report extensive anomalies identified in seismicity parameters at different energy levels which were observed during the precursory process of the Karymskii seismovolcanic crisis of January 1–2, 1996. The seismicity of different energies includes earthquakes contained in the Kamchatka regional catalog and seismic noise (amplitudes of 10^?9–10^?12 m, frequencies of a few tens of hertz), which is a manifestation of the seismic process in the lowest energy range. The parameters of background seismicity are considered in retrospect using techniques for analyzing the dynamics of the seismic process: RTL and the Z function. Microseismicity is examined using these authors’ own method based on monitoring the response of high frequency seismic noise to tidal excitation     

Interrelation among several important links in seismic risk analysis

Introduction In the probability analysis method of seismic risk considering time-space inhomogeneity of seismic activity and adopted commonly in China (State Seismological Bureau, 1996) (called in-homogeneous distribution model for short), the division of seismic statistical regions, delimitation of potential seismic sources and estimation of seismicity parameters are the main links that affect significantly the estimation of ground motion parameters of a site. HUANG and WU (2005) studied …     

Source Characteristics of the 22 January 2003 M w?=?7.5 Tecom��n, Mexico, Earthquake: New Insights

Aftershock locations, source parameters and slip distribution in the coupling zone between the overriding North American and subducted Rivera and Cocos plates were calculated for the 22 January 2003 Tecomán earthquake. Aftershock locations lie north of the El Gordo Graben with a northwest-southeast trend along the coast and superimposed on the rupture areas of the 1932 (M _w?=?8.2) and 1995 (M _w?=?8.0) earthquakes. The Tecomán earthquake ruptured the northwest sector of the Colima gap, however, half of the gap remains unbroken. The aftershock area has a rectangular shape of 42?±?2 by 56?±?2?km with a shallow dip of roughly 12° of the Wadati-Benioff zone. Fault geometry calculated with the Náb??lek (1984) inversion procedure is: (strike, dip, rake)?=?(277°, 27°, 78°). From the teleseimic body wave spectra and assuming a circular fault model, we estimated source duration of 20?±?2?s, a stress drop of 5.4?±?2.5?MPa and a seismic moment of 2.7?±?.7?×?10²⁰?Nm. The spatial slip distribution on the fault plane was estimated using new additional near field strong motion data (54?km from the epicenter). We confirm their main conclusions, however we found four zones of seismic moment release clearly separated. One of them, not well defined before, is located toward the coast down dip. This observation is the result of adding new data in the inversion. We calculated a maximum slip of 3.2?m, a source duration of 30?s and a seismic moment of 1.88?×?10²⁰?Nm.     

An Evaluation of Coulomb Stress Changes from Earthquake Productivity Variations in the Western Gulf of Corinth,Greece

Spatial and temporal evolution of the stress field in the seismically active and well-monitored area of the western Gulf of Corinth, Greece, is investigated. The highly accurate and vast regional catalogues were used for inverting seismicity rate changes into stress variation using a rate/state-dependent friction model. After explicitly determining the physical quantities incorporated in the model (characteristic relaxation time, fault constitutive parameters, and reference seismicity rates), we looked for stress changes across space and over time and their possible association with earthquake clustering and fault interactions. We focused our attention on the Efpalio doublet of January 2010 (M = 5.5 and M = 5.4), with a high aftershock productivity, and attempted to reproduce and interpret stress changes prior to and after the initiation of this seismicity burst. The spatial distribution of stress changes was evaluated after smoothing the seismological data by means of a probability density function (PDF). The inverted stress calculations were compared with the calculations derived from an independent approach (elastic dislocation model) and this comparison was quantified. The results of the two methods are in good agreement (up to 80 %) in the far field, with the inversion technique providing more robust results in the near field, where they are more sensitive to the uncertainties of coseismic slip distribution. It is worth mentioning that the stress inversion model proved to be a very sensitive stress meter, able to detect even small stress changes correlated with spatio–temporal earthquake clustering. Data analysis was attempted from 1975 onwards to simulate the stress changes associated with stronger earthquakes over a longer time span. This approach revealed that only M > 5.5 events induce considerable stress variations, although in some cases there was no evidence for such stress changes even after an M > 5.5 earthquake.     

A Probabilistic Assessment of Earthquake Hazard Parameters in NW Himalaya and the Adjoining Regions

The maximum likelihood estimation method is applied to study the geographical distribution of earthquake hazard parameters and seismicity in 28 seismogenic source zones of NW Himalaya and the adjoining regions. For this purpose, we have prepared a reliable, homogeneous and complete earthquake catalogue during the period 1500–2010. The technique used here allows the data to contain either historical or instrumental era or even a combination of the both. In this study, the earthquake hazard parameters, which include maximum regional magnitude (M _max), mean seismic activity rate (λ), the parameter b (or β?=?b/log e) of Gutenberg–Richter (G–R) frequency-magnitude relationship, the return periods of earthquakes with a certain threshold magnitude along with their probabilities of occurrences have been calculated using only instrumental earthquake data during the period 1900–2010. The uncertainties in magnitude have been also taken into consideration during the calculation of hazard parameters. The earthquake hazard in the whole NW Himalaya region has been calculated in 28 seismogenic source zones delineated on the basis of seismicity level, tectonics and focal mechanism. The annual probability of exceedance of earthquake (activity rate) of certain magnitude is also calculated for all seismogenic source zones. The obtained earthquake hazard parameters were geographically distributed in all 28 seismogenic source zones to analyze the spatial variation of localized seismicity parameters. It is observed that seismic hazard level is high in Quetta-Kirthar-Sulaiman region in Pakistan, Hindukush-Pamir Himalaya region and Uttarkashi-Chamoli region in Himalayan Frontal Thrust belt. The source zones that are expected to have maximum regional magnitude (M _max) of more than 8.0 are Quetta, southern Pamir, Caucasus and Kashmir-Himanchal Pradesh which have experienced such magnitude of earthquakes in the past. It is observed that seismic hazard level varies spatially from one zone to another which suggests that the examined regions have high crustal heterogeneity and seismotectonic complexity.