Seismotectonic deformations and stress fields in the fault zone of the 2003 Chuya earthquake, Ms = 7.5, Gorny Altai

The seismotectonic deformations related to the Chuya earthquake September 27, 2003 in the Gorny Altai (M_s = 7.5) are studied in detail. These deformations developed as advanced systems of R-and R’-shears, gash fractures, and compression structural features in loose sediments. In bedrocks, the older shear zones were reactivated, the previously existing fractures were renewed and propagated further, and new faults and crush zones were formed. The system of seismic dislocations is a fault zone no less than 4 km wide that extends in the northwestern direction. As follows from the structural elements that reveal a systematic mutual orientation, the internal structure of this zone is typical of a right-lateral strike-slip fault. The initial stress field that led to the development of the entire assemblage of seismotectonic deformations related to the Chuya earthquake corresponds to the strike-slip type with the NNW, almost meridional direction of compression axis (σ₁) and the ENE, almost latitudinal direction of the tension axis (σ₃). The local variations of the stress state were expressed in an insignificant shift of σ₁ to the northwest or northeast, in the short-term change of relative stress values with retention of their spatial orientation, and in the increasing inclination of σ₁ in front of the previously existing fault. The comparison of the internal structure of the seismotectonic fault zone with a tectonophysical model of faulting in large continental systems with a right-lateral offset indicates that the distribution of the advanced faults corresponds to the late stage of faulting, when the main fault is still not formed completely, but its particular segments are already developed distinctly. It is shown that at high rates of displacement the structural features in markedly different rocks develop according to the general laws of solids’ deformation even near the day surface.     

Block displacement fields in the Altai-Sayan region and effective rheologic parameters of the Earth’s crust

The paper is focused on recent displacement rates in the Altai-Sayan region, obtained by hydroleveling, leveling, and satellite geodesy. Effective elastic moduli and viscosity parameters of the crust are used in the modeling of coseismic and tectonic processes. The elastic moduli are determined from measurements of periodic vertical displacements during seasonal loadings of the Sayano-Shushenskaya hydropower plant. We present the results of the modeling of coseismic displacements during the earthquakes of 10 February 2011 (M = 6.1) and 27 December 2011 (M = 6.7) in Tuva and West Sayan. The results of GPS determinations for postseismic displacements in the Chuya earthquake zone (Gorny Altai, 27 September 2003, M = 7.5) are analyzed; models for the geologic medium are selected; and its effective viscosity is estimated. The tectonic component of the recent crustal displacements in the Altai-Sayan region is defined.     

Modeling Cenozoic crustal deformation in Gorny Altai

The Altai lithospheric structure has been generally understood due to available high-resolution digital models. As a further step in modeling, we have simulated the structure of southeastern Altai as interaction of eight blocks which comprise or surround the Chuya and Kurai basins, proceeding from the basic configuration of blocks and earthquake mechanisms. Should the stresses in the system remain invariable, the western periphery of the Kurai basin will deform to let the Uimen-Sumulta fault join the Chuya (western end of Tolbonur) fault and evolve further as a single shear zone. The best fit model was one with slip along a single border fault in the middle of the area between two rheologically different terranes. This setting corresponds to a fault boundary between the more plastic Gorny Altai and more rigid Teletskoe-Chulyshman domains, which is consistent with current crustal movements from GPS data. In addition to scientific significance, models of this kind have practical applications as they highlight areas of stress buildup prone to release in large earthquakes. The new approach was applied to simulate the stress and strain patterns of central and southeastern Gorny Altai, and the models were tested against available geomorphological and seismotectonic data.     

Earthquake hazard and risk assessment based on unified scaling law for earthquakes: Altai–Sayan Region

We apply the general concept of seismic risk analysis based on morphostructural analysis of the territory, pattern recognition of earthquake-prone nodes, and the Unified Scaling Law for Earthquakes, USLE, in another seismic region of Russia to the west from Lake Baikal, i.e., Altai–Sayan Region. The USLE generalizes the empirical Gutenberg–Richter relationship making use of apparently fractal distribution of earthquake sources of different size: \( \log_{10} N\left( {M,L} \right)\, = \,A\, + \,B \cdot \left( {5\, - \,M} \right)\, + \,C \cdot \log_{10} L, \) where N (M, L) is the expected annual number of earthquakes of a certain magnitude M within an seismically prone area of linear dimension L. The local estimates of A, B, and C allow determination of the expected maximum credible magnitude in a given time interval and the associated spread around ground shaking parameters (e.g., peak ground acceleration, PGA, or macroseismic intensity, I₀). Compilation of the corresponding seismic hazard map of Altai–Sayan Region and its rigorous testing against the available seismic evidences in the past is used to model regional maps of specific earthquake risks for population, cities, and infrastructures.     

Probabilistic seismic hazard assessment in the Constantine region,Northeast of Algeria

This paper presents a seismic hazard evaluation and develops an earthquake catalogue for the Constantine region over the period from 1357 to 2014. The study contributes to the improvement of seismic risk management by evaluating the seismic hazards in Northeast Algeria. A regional seismicity analysis was conducted based on reliable earthquake data obtained from various agencies (CRAAG, IGN, USGS and ISC). All magnitudes (M _l, m _b) and intensities (I ₀, I _MM, I _MSK and I _EMS) were converted to M _s magnitudes using the appropriate relationships. Earthquake hazard maps were created for the Constantine region. These maps were estimated in terms of spectral acceleration (SA) at periods of 0.1, 0.2, 0.5, 0.7, 0.9, 1.0, 1.5 and 2.0 s. Five seismogenic zones are proposed. This new method differs from the conventional method because it incorporates earthquake magnitude uncertainty and mixed datasets containing large historical events and recent data. The method can be used to estimate the b value of the Gutenberg-Richter relationship, annual activity rate λ(M) of an event and maximum possible magnitude M _max using incomplete and heterogeneous data files. In addition, an earthquake is considered a Poisson with an annual activity rate λ and with a doubly truncated exponential earthquake magnitude distribution. Map of seismic hazard and an earthquake catalogue, graphs and maps were created using geographic information systems (GIS), the Z-map code version 6 and Crisis software 2012.     

Coseismic landslides triggered by the 8th August 2017 <Emphasis Type="Italic">M</Emphasis><Subscript>s</Subscript> 7.0 Jiuzhaigou earthquake (Sichuan,China): factors controlling their spatial distribution and implications for the seismogenic blind fault identification

On 8th August 2017, a magnitude M_s 7.0 earthquake struck the County of Jiuzhaigou, in Sichuan Province, China. It was the third M_s ≥?7.0 earthquake in the Longmenshan area in the last decade, after the 2008 M_s 8.0 Wenchuan earthquake and the 2013 M_s 7.0 Lushan earthquake. The event did not produce any evident surface rupture but triggered significant mass wasting. Based on a large set of pre- and post-earthquake high-resolution satellite images (SPOT-5, Gaofen-1 and Gaofen-2) as well as on 0.2-m-resolution UAV photographs, a polygon-based interpretation of the coseismic landslides was carried out. In total, 1883 landslides were identified, covering an area of 8.11 km², with an estimated total volume in the order of 25–30?×?10⁶ m³. The total landslide area was lower than that produced by other earthquakes of similar magnitude with strike-slip motion, possibly because of the limited surface rupture. The spatial distribution of the landslides was correlated statistically to a number of seismic, terrain and geological factors, to evaluate the landslide susceptibility at regional scale and to identify the most typical characteristics of the coseismic failures. The landslides, mainly small-scale rockfalls and rock/debris slides, occurred mostly along two NE-SW-oriented valleys near the epicentre. Comparatively, high landslide density was found at locations where the landform evolves from upper, broad valleys to lower, deep-cut gorges. The spatial distribution of the coseismic landslides did not seem correlated to the location of any known active faults. On the contrary, it revealed that a previously-unknown blind fault segment—which is possibly the north-western extension of the Huya fault—is the plausible seismogenic fault. This finding is consistent with what hypothesised on the basis of field observations and ground displacements.     

Source mechanism and parameters of the 19 October 2012 earthquake,northern Egyptian continental margin

The 19 October 2012 earthquake (M _L = 5.1) occurred in the northern continental margin of Egypt within the Nile Cone at latitude 32.35° N and longitude 31.27° E. The quake was felt over a wide area in north Egypt and East Mediterranean countries, but no casualties have been reported. This area had experienced the large earthquake (Ms = 6.7) of 12 September 1955. The fault plane solution of the 19 October 2012 earthquake is here presented based on the digital seismograms recorded by the Egyptian National Seismological Network (ENSN) and other regional seismic stations. The analysis is carried out using the well-known techniques of first motion polarities of P-wave and the amplitude ratios of P-, SH-, and SV-waves with lower hemisphere projection. The fault plane solution based on the first P-wave onset demonstrates a left lateral strike-slip faulting mechanism, while the solution based on both P-wave polarities and amplitude ratios of P-, SH-, and SV-waves reveals a reverse fault with strike-slip component trending NW–SE to NE–SW, in conformity with the N–S compression along the Hellenic Arc convergence zone. Following the Brune’s model, the source dynamic parameters for the 19 October 2012 earthquake are estimated as corner frequency = 1.47 Hz, fault radius = 0.7 km, stress drop = 22.1 MPa, seismic moment = 2.80E + 16 Nm, and moment magnitude M _w = 4.9. These parameters may provide important quantitative information for the seismic hazard assessment studies.     

Evaluating of the earthquake hazard parameters with Bayesian method for the different seismic source regions of the North Anatolian Fault Zone

The earthquake hazard parameters and earthquake occurrence probabilities are computed for the different regions of the North Anatolia Fault Zone (NAFZ) using Bayesian method. A homogenous earthquake catalog for M _S magnitude which is equal or larger than 4.0 is used for a time period between 1900 and 2015. Only two historical earthquakes (1766, M _S = 7. 3 and 1897, M _S = 7. 0) are included in Region 2 (Marmara Region) where a large earthquake is expected in the near future since no large earthquake has been observed for the instrumental period. In order to evaluate earthquake hazard parameters for next 5, 10, 20, 50, 100 years, M _max (maximum regional magnitude), β value, λ (seismic activity or density) are computed for the different regions of NAFZ. The computed M _max values are changed between 7.11 and 7.89. While the highest magnitude value is calculated in the Region 9 related to Tokat-Erzincan, the lowest value in the Region 10 including the eastern of Erzincan. The “quantiles” of “apparent” and “true” magnitudes of future time intervals of 5, 10, 20, 50, and 100 years are calculated for confidence limits of probability levels of 50, 70 and 90 % of the 10 different seismic source regions. The region between Tokat and Erzincan has earthquake hazard level according to the determined parameters. In this region the expected maximum earthquake size is 7.8 with 90 % occurrence probability in next 100 years. While the regional M _max value of Marmara Region is computed as 7.61, expected maximum earthquake size is 7.37 with 90 % occurrence probability in next 100 years.     

Ecological-geodynamic evaluation of the Chuya earthquake

Disruptions of the Gornyi Altai ecologic-geological systems due to the Chuya earthquake were examined. The energy bond between abiotic Earth spheres (the lithosphere and atmosphere) and biota were investigated during the period of seismic activity of the Earth’s mantle, particularly with respect to population morbidity.     

Teleseismic finite-fault inversion of two <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript> = 6.4 earthquakes along the East Anatolian Fault Zone in Turkey: the 1998 Adana and 2003 Bingöl earthquakes

The East Anatolian Fault Zone is a continental transform fault accommodating westward motion of the Anatolian fault. This study aims to investigate the source properties of two moderately large and damaging earthquakes which occurred along the transform fault in the last two decades using the teleseismic broadband P and SH body waveforms. The first earthquake, the 27 June 1998 Adana earthquake, occurred beneath the Adana basin, located close to the eastern extreme of Turkey’s Mediterranean coast. The faulting associated with the 1998 Adana earthquake is unilateral to the NE and confined to depths below 15 km with a length of 30 km along the strike (53°) and a dipping of 81° SE. The fixed-rake models fit the data less well than the variable-rake model. The main slip area centered at depth of about 27 km and to the NE of the hypocenter, covering a circular area of 10 km in diameter with a peak slip of about 60 cm. The slip model yields a seismic moment of 3.5?×?10¹⁸ N-m (M_w???6.4). The second earthquake, the 1 May 2003 Bingöl earthquake, occurred along a dextral conjugate fault of the East Anatolian Fault Zone. The preferred slip model with a seismic moment of 4.1?×?10¹⁸ N-m (M_w???6.4) suggests that the rupture was unilateral toward SE and was controlled by a failure of large asperity roughly circular in shape and centered at a depth of 5 km with peak displacement of about 55 cm. Our results suggest that the 1998 Adana earthquake did not occur on the mapped Göksun Yakap?nar Fault Zone but rather on a SE dipping unmapped fault that may be a split fault of it and buried under the thick (about 6 km) deposits of the Adana basin. For the 2003 Bingöl earthquake, the final slip model requires a rupture plane having 15° different strike than the most possible mapped fault.     

Petrology of volcanic and plutonic rocks from the Uimen-Lebed’ terrain,Gorny Altai

The Uimen-Lebed’ volcanoplutonic terrane is located at the junction of the Gorny Altai, Gornaya Shoriya, and western Sayan structures and is part of the Devonian-Early Carbonaceous Salair-Altai volcanoplutonic belt. The volcanic facies of the terrane composes the contrasting Nyrnin-Sagan Group, which includes basalt-basaltic andesite and basalt-rhyolite associations. The plutonic facies makes up the multiplet Elekmonar Group, which includes two independent complexes: monzogabbro-monzodiorite-granodiorite-granite and granodiorite-granite-leucogranite. The volcanic and plutonic rocks are asymmetrically distributed: volcanic sequences fill inherited depressions in the eastern part of the terrane, whereas plutonic complexes are located in its western part at the fault system branching from the transregional Kuznetsk-Teletsk-Kurai fault zone. The basalts of the Nyrnin-Sagan Group show geochemical signatures of both suprasubduction and rift-related rocks. The evolution of basaltoid magmatism reflects the formation and development of a suprasubduction mantle wedge in the inner part of an active continental margin accompanied by the influence of an intraplate mantle source. The silicic volcanism was generated under lower crustal conditions (P > 10 kbar) at the expense of metabasic materials and was accompanied by the influx of potassium into the anatectic zones. The gabbroids of the Elekmonar Group show suprasubduction geochemical features and no signatures of rift-related structures. The composition of the Elekmonar granitoids indicates significantly shallower (compared with the silicic volcanics) depths of their generation. The Uimen-Lebed’ volcanoplutonic terrane in the northeastern part of Gorny Altai was formed in the inner part of an active continental margin of the Andean type. Its magmatic complexes were formed over a considerable time range, from the early Emsian, when the formation of the active continental margin began, to the end of the Eifelian or, more likely, the beginning of the Givetian stage.     

Site response of the Ganges basin inferred from re-evaluated macroseismic observations from the 1897 Shillong, 1905 Kangra,and 1934 Nepal earthquakes

We analyze previously published geodetic data and intensity values for the M _s = 8.1 Shillong (1897), M _s = 7.8 Kangra (1905), and M _s = 8.2 Nepal/Bihar (1934) earthquakes to investigate the rupture zones of these earthquakes as well as the amplification of ground motions throughout the Punjab, Ganges and Brahmaputra valleys. For each earthquake we subtract the observed MSK intensities from a synthetic intensity derived from an inferred planar rupture model of the earthquake, combined with an attenuation function derived from instrumentally recorded earthquakes. The resulting residuals are contoured to identify regions of anomalous intensity caused primarily by local site effects. Observations indicative of liquefaction are treated separately from other indications of shaking severity lest they inflate inferred residual shaking estimates. Despite this precaution we find that intensites are 1–3 units higher near the major rivers, as well as at the edges of the Ganges basin. We find evidence for a post-critical Moho reflection from the 1897 and 1905 earthquakes that raises intensities 1–2 units at distances of the order of 150 km from the rupture zone, and we find that the 1905 earthquake triggered a substantial subsequent earthquake at Dehra Dun, at a distance of approximately 150 km. Four or more M = 8 earthquakes are apparently overdue in the region based on seismic moment summation in the past 500 years. Results from the current study permit anticipated intensities in these future earthquakes to be refined to incorporate site effects derived from dense macroseismic data.     

Seismic anisotropy of the mantle beneath Eastern Asia based on <Emphasis Type="Italic">ScS</Emphasis> and <Emphasis Type="Italic">S</Emphasis> waves from deep-focus earthquakes

The seismic anisotropy of the mantle is studied based on the data of S and ScS waves from earthquakes occurred in the mantle transition zone over the period of 2007–2013 and recorded by seismic stations in the continental margin of Asia, on Sakhalin Island, and in the southern part of the Kamchatka Peninsula. The measurements of the azimuths of polarization of the fast S and ScS waves in the continental margin of Asia show that they are predominantly oriented in the E–SE directions. Based on the distribution of the shear wave splitting parameters, the symmetry of the medium can be described in terms of a transversely isotropic model with a horizontal symmetry axis and may correspond to horizontal flow in the upper mantle beneath the Amur Plate. The fast azimuths of polarization of ScS wave, which were determined to be of N–NE directions in the northern area of Sakhalin Island and in the continental part of Asia, may correspond to an inclined flow under the conditions of oblique subduction and complex geometry of the downgoing Pacific Plate. In the south of the Kamchatka Peninsula, the S- and ScS-wave azimuths of polarization from the M 8.4 Sea of Okhotsk earthquake are determined to be oriented along the direction of the Pacific Plate motion. The fast-S-wave azimuths of polarization from the aftershocks of the Sea of Okhotsk earthquake and from other large events of 2008–2009 are determined to be nearly parallel to the motion trend of the Pacific Plate, but orthogonal to it for the events of 2008–2009. On the basis of the distribution of azimuths of polarization of the fast S waves, the symmetry of the medium can be described in terms of a transversely isotropic model with the symmetry axis inclined orthogonally to the plane of downgoing plate and oriented westward orthogonally to the trench strike.     

Geometry of the fault zone of the 2003 Ms = 7.5 Chuya earthquake and associated stress fields, Gorny Altai

The co-seismic deformations produced during the September 27, 2003 Chuya earthquake (Ms = 7.5) that affected the Gorny Altai, Russia, are described and discussed along a 30 km long segment. The co-seismic deformations have manifested themselves both in unconsolidated sediments as R- and R′-shears, extension fractures and contraction structures, and in bedrock as the reactivation of preexisting schistosity zones and individual fractures, as well as development of new ruptures and coarse crushing zones. It has been established that the pattern of earthquake ruptures represents a typical fault zone trending NW–SE with a width reaching 4–5 km and a dextral strike–slip kinematics. The initial stress field that produced the whole structural pattern of co-seismic deformations during the Chuya earthquake, is associated with a transcurrent regime with a NNW–SSE, almost N–S, trending of compressional stress axis (σ₁), and a ENE–WSW, almost E–W, trending of tensional stress axis (σ₃). The state of stress in the newly-formed fault zone is relatively uniform. The local stress variations are expressed in insignificant deviation of σ₁ from N–S to NW–SE or NE–SW, in short-term fluctuations of relative stress values in keeping their spatial orientations, or in a local increase of the plunge angle of the σ₁. The geometry of the fault zone associated with the Chuya earthquake has been compared with the mechanical model of fracturing in large continental fault zones with dextral strike–slip kinematics. It is apparent that the observed fracture pattern corresponds to the late disjunctive stage of faulting when the master fault is not fully developed but its segments are already clearly defined. It has been shown that fracturing in widely different rocks follows the common laws of the deformation of solid bodies, even close to the Earth surface, and with high rates of movements.     

Unknown large ancient earthquakes along the Kurai fault zone (Gorny Altai): new results of palaeoseismological and archaeoseismological studies

Palaeoseismological and archaeoseismological studies in the Kurai fault zone, along which the Kurai Range is thrust onto Cenozoic deposits of the Chuya intramontane basin, led to the identification of a long reverse fault scarp 8.0 m high. The scarp segments are primary seismic deformations of large ancient earthquakes. The scarp’s morphology, results of trenching investigations, and deformations of Neogene deposits indicate a thrusting of the piedmont plain onto the Kurai Range, which is unique for the Gorny Altai. Similarly for Northern Tien Shan, we explain this by the formation of both a thrust transporting the mountain range onto the depression and a branching thrust dislocation that forms the detected fault scarp. In a trench made in one of the scarp segments, we identified the parameters of the seismogenic fault – a thrust with a 30° dipping plane. The reconstructed displacement along the fault plane is 4.8 m and the vertical displacement is 2.4 m, which indicates a 7.2–7.6 magnitude of the ancient earthquake. The ¹⁴C age of the humus-rich loamy sand from the lower part of the colluvial wedge constrains the age of the earthquake at 3403–3059 years BP. Younger than 2500 years seismogenic displacements along the fault scarp are indicated by deformations of cairn structures of the Turalu–Dzhyurt-III burial mound, which was previously dated as iron age between the second half of I BC and I AD.     

Seismic hazard scenario and attenuation model of the Garhwal Himalaya using near-field synthesis from weak motion seismometry

In this paper, we present a seismic hazard scenario for the Garhwal region of the north-western Himalayan range, in terms of the horizontal Peak Ground Acceleration. The scenario earthquake of moment magnitude M _w 8.5 has a 10% exceedance probability over the next 50 years. These estimates, the first for the region, were calculated through a stepwise process based on:

• An estimation of the Maximum Credible Earthquake from the seismicity of the region and Global Seismic Hazard Assessment Program considerations, and
• four seismotectonic parameters abstracted from near field weak-motion data recorded at five stations installed in Chamoli District of the Garhwal region in the aftermath of the 1999 Chamoli earthquake. The latter include
• The frequency dependent power law for the shear wave quality factor, Q _S
• the site amplification at each station using horizontal-to-vertical-spectral ratio and generalized inversion technique
• source parameters of various events recorded by the array and application of the resulting relations between the scalar seismic moment M ₀ (dyne-cm) and moment magnitude M _w and the corner frequency, ? _c (Hz) and moment magnitude M _w to simulate spectral acceleration due to higher magnitude events corresponding to the estimated Maximum Credible Earthquake, and
• regional and site specific local spectral attenuation relations at different geometrically central frequencies in the low, moderate and high frequency bands.

     

The Investigation Results of the April 12, 2014, <Emphasis Type="Italic">M</Emphasis> = 4.5 Primorye Earthquake (Far Eastern Russia)

Primorye is a region with quite moderate shallow seismicity which has been insufficiently investigated so far in this respect. Based on the obtained instrumental data of regional seismic networks and macroseismic data collected in southwestern Primorye on the crustal earthquake with M = 4.5 occurred on April 12, 2014, we have first succeeded in determining the hypocenter parameters and the focal mechanism of the mainshock of this shallow earthquake and estimating the hypocenter parameters of the following aftershock.     

Seismic hazard and probability assessment of Kashmir valley,northwest Himalaya,India

Seismic hazard analysis of the northwest Himalayan belt was carried out by using extreme value theory (EVT). The rate of seismicity (a value) and recurrence intervals with the given earthquake magnitude (b value) was calculated from the observed data using Gutenberg–Richter Law. The statistical evaluation of 12,125 events from 1902 to 2017 shows the increasing trend in their inter-arrival times. The frequency–magnitude relation exhibits a linear downslope trend with negative slope of 0.8277 and positive intercept of 4.6977. The empirical results showed that the annual risk probability of high magnitude earthquake M?≥?7.7 in 50 years is 88% with recurrence period of 47 years, probability of M?≤?7.5 in 50 years is 97% with recurrence period of 27 years, and probability of M?≤?6.5 in 50 years is 100% with recurrence period of 4 years. Kashmir valley, located in the NW Himalaya, encompasses a peculiar tectonic and structural setup. The patterns of the present and historical seismicity records of the valley suggest a long-term strain accumulation along NNW and SSE extensions with the decline in the seismic gap, posing a potential threat of earthquakes in the future. The Kashmir valley is characterized by the typical lithological, tectono-geomorphic, geotechnical, hydrogeological and socioeconomic settings that augment the earthquake vulnerability associated with the seismicity of the region. The cumulative impact of the various influencing parameters therefore exacerbates the seismic hazard risk of the valley to future earthquake events.     

Nature of the macroseismic paradox of the deep-focus earthquake in the Sea of Okhotsk on May 24, 2013 (<Emphasis Type="Italic">M</Emphasis> <Subscript> <Emphasis Type="Italic">w</Emphasis> </Subscript> = 8.3)

We analyzed macroseismic data and considered the effect of extremely long range propagation of sensible shocks during the deep-focus earthquake in the Sea of Okhotsk on May 24, 2013 (M_w = 8.3). In order to explain this effect, we formulated and qualitatively solved the problem of superposition of P-waves over the radial mode ₀S₀ of the natural oscillations of the Earth during this earthquake. Our results confirmed the possibility of such an interpretation of the observed macroseismic effect and also allowed us to explain the fact of anomalously low decay of seismic disturbances with distance.     

Fault rupture and stress changes associated with the November 27, 2005 Qeshm Island (Iran) earthquake (<Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> = 6.0)

The November 27, 2005 Qeshm Island earthquake (M_w 6.0) occurred along the Zagros Thrust and Fold Belt which accommodates about half of the deformation caused by the Arabian and Eurasian Plates convergence. As typical for the belt, the earthquake was associated with buried reverse faulting and produced no surface rupture. Here, teleseismic broadband P velocity waveforms of the earthquake are inverted to obtain coseismic finite-fault slip distribution of the earthquake. It is obtained that rupture was controlled by failure of a single asperity with largest displacement of approximately 0.6 m, which occurred at a depth of 9 km. The slip model indicated radial rupture propagation from the hypocentre and confirmed blind reverse faulting within deeper part (below the depth of 6 km) of the sedimentary cover above the Hormuz Salt, lying between the cover and the basement, releasing a seismic moment of about 1.3?×?10¹⁸ Nm (M_W?=?6.0). The results also confirm that the Hormuz Salt behaves as a barrier for rupture propagation to the basement below and occurrence of the aftershock activity downdip from the rupture within the Hormuz Salt. Calculated Coulomb stress variations caused by the coseismic rupture indicates stress coupling between the 2005 Qeshm Island earthquake and both the largest aftershock several hours later and the 2008 Qeshm Island earthquake (M_W?=?5.9). The stress calculations further indicated stress load at the depth range (15–20 km) of the well-located aftershocks, corresponding to depths of the Hormuz Salt and top of the basement and providing plausible explanation for occurrence of the aftershocks within those layers.