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1.
We present the estimated source parameters from SH-wave spectral modeling of selected 463 aftershocks (2002–06) of the 26 January 2001 Bhuj earthquake, the well-recorded largest continental intraplate earthquake. The estimated seismic moment (Mo), corner frequency (fc), source radius (r) and stress drop (Δσ) for aftershocks of moment magnitude 1.7 to 5.6 range from 3.55×1011 to 2.84×1017 N-m, 1.3 to 11.83 Hz, 107 to 1515 m and 0.13 to 26.7 MPa, respectively, while the errors in fc and Δσ are found to be 1.1 Hz and 1.1 MPa, respectively. We also notice that the near surface attenuation factor (k) values vary from 0.02 to 0.03. Our estimates reveal that the stress drop values show more scatter (Mo0.5 to 1 is proportional to Δσ) toward the larger Mo values (≥1014.5 N-m), while they show a more systematic nature (Mo3 is proportional to Δσ) for smaller Mo values (<1014.5 N-m), which can be explained as a consequence of a nearly constant rupture radius for smaller aftershocks in the region. The large stress drops (= 10 MPa) associated with events on the north Wagad fault (at 15–30 km depth) and Gedi fault (at 3–15 km depth) can be attributed to the large stress developed at hypocentral depths as a result of high fluid pressure and the presence of mafic intrusive bodies beneath these two fault zones. 相似文献
2.
Locally recorded data for eighteen aftershocks of a magnitude(mb) 4.6 earthquake occurring near Ukhimath in the Garhwal Himalaya were analysed. A master event technique was adopted to locate
seventeen individual aftershock hypocentres relative to the hypocentre of the eighteenth aftershock chosen as the master event.
The aftershock epicentres define an approximately 30 km2 rupture zone commensurate with the magnitude of the earthquake. The distribution of epicentres within this zone and the limited
amount of first motion data support the view that a group of parallel, sub-vertical, sinistral strike-slip faults oriented
N46°, transverse to the regional NW-SE trend of the Garhwal Himalaya, was involved in this seismic episode. Since the estimated
focal depth range for aftershocks of this sequence is 3–14 km, we infer that this transverse fault zone extends through the
upper crustal layer to a depth of 14 km at least. 相似文献
3.
The Jiashian earthquake (ML 6.4) occurred on 4 March 2010. It was the largest inland event in southern Taiwan of 2010. The mainshock location was unexpected since it occurred in an area with relatively low background seismicity. In addition, reports of earthquake focal mechanisms do not fit with any known active fault geometry. In order to understand the origin of this earthquake, especially its rupture process, we perform a joint source inversion by using teleseismic body wave, GPS coseismic displacements and near field ground motion data. In this study, we considered a northwest–southeast trending fault with a northeast dip retrieved from GPS coseismic data and aftershocks distribution. To analyze the detailed slip distribution in space and time, we used near field 3D Green’s functions provided by spectral-element method and a full time–space inversion technique. We find a complex rupture process with several slip patches distributed inside two main asperities. The slip map reveals a mean slip of 12.9 cm for a maximum slip of 27.3 cm leading to a Mw 6.47 for this event. The rupture initiates in the deepest portion of the fault at 20 km depth, and propagated upward up to 2 km depth to form the two asperities. The source time function of this event revealed two pulses corresponding to the two asperities, for a total duration time of about 16 s. Most aftershocks occurred near the upper boundary of the deepest asperity while no aftershocks are located close to the shallowest one. We infer that the locations of these slip patches are related to the surrounding fault systems that may have restricted the rupture propagation during the earthquake. 相似文献
4.
Earthquakes in Kenya are common along the Kenya Rift Valley because of the slow divergent movement of the rift and hydrothermal processes in the geothermal fields. This implies slow but continuous radiation of seismic energy, which relieves stress in the subsurface rocks. On the contrary, the NW-SE trending rift/fault zones such as the Aswa-Nyangia fault zone and the Muglad-Anza-Lamu rift zone are the likely sites of major earthquakes in Kenya and the East African region. These rift/fault zones have been the sites of a number of strong earthquakes in the past such as the M w = 7.2 southern Sudan earthquake of 20 May 1990 and aftershocks of M w = 6.5 and 7.1 on 24 May 1990, the 1937 M s = 6.1 earthquake north of Lake Turkana close to the Kenya-Ethiopian border, and the 1913 M s = 6.0 Turkana earthquake, among others. Source parameters of the 20 May 1990 southern Sudan earthquake show that this earthquake consists of only one event on a fault having strike, dip, and rake of 315°, 84°, and ?3°. The fault plane is characterized by a left-lateral strike slip fault mechanism. The focal depth for this earthquake is 12.1 km, seismic moment M o = 7.65 × 1019 Nm, and moment magnitude, M w = 7.19 (?7.2). The fault rupture started 15 s earlier and lasted for 17 s along a fault plane having dimensions of ?60 km × 40 km. The average fault dislocation is 1.1 m, and the stress drop, ?σ, is 1.63 MPa. The distribution of historical earthquakes (M w ≥ 5) from southern Sudan through central Kenya generally shows a NW-SE alignment of epicenters. On a local scale in Kenya, the NW–SE alignment of epicenters is characterized by earthquakes of local magnitude M l ≤ 4.0, except the 1928 Subukia earthquake (M s = 6.9) in central Kenya. This NW–SE alignment of epicenters is consistent with the trend of the Aswa-Nyangia Fault Zone, from southern Sudan through central Kenya and further southwards into the Indian Ocean. We therefore conclude that the NW–SE trending rift/fault zones are sites of strong earthquakes likely to pose the greatest earthquake hazard in Kenya and the East African region in general. 相似文献
5.
An earthquake of magnitude 6.9 (M w) occurred in the Sikkim region of India on September 18, 2011. This earthquake is recorded on strong-motion network in Uttarakhand Himalaya located about 900 km away from the epicenter of this earthquake. In this paper acceleration record from six far-field stations has been used to compute the source parameters of this earthquake. The acceleration spectra of ground motion at these far-field stations are strongly affected by both local site effects and near-site anelastic attenuation. In the present work the spectrum of S-phase recorded at these far-field stations has been corrected for anelastic attenuation at both source and site and the site amplification terms. Site amplifications at different stations and near-site shear wave attenuation factor have been computed by the technique of inversion of acceleration spectra given by Joshi et al. (Pure Appl Geophys 169:1821–1845, 2012a). For estimation of site amplification and shear wave quality factor [Q β (f)] at the recording sites, ten local events recorded at various stations between July 2011 and December 2011 have been used. The obtained source spectrum from acceleration records is compared with the theoretical source spectrum defined by Brune (J Geophys Res 76:5002, 1970) at each station for both horizontal components of the records. Iterative forward modeling of theoretical source spectrum gives the average estimate of seismic moment (M o), source radius (r o) and stress drop (Δσ) as (3.2 ± 0.8) × 1026 dyne cm, 13.3 ± 0.8 km and 59.2 ± 8.8 bars, respectively, for the Sikkim earthquake of September 18, 2011. 相似文献
6.
7.
Mustafa Toker 《Central European Journal of Geosciences》2013,5(3):423-434
The Van earthquake (M W 7.1, 23 October 2011) in E-Anatolia is typical representative of intraplate earthquakes. Its thrust focal character and aftershock seismicity pattern indicate the most prominent type of compound earthquakes due to its multifractal dynamic complexity and uneven compressional nature, ever seen all over Turkey. Seismicity pattern of aftershocks appears to be invariably complex in its overall characteristics of aligned clustering events. The population and distribution of the aftershock events clearly exhibit spatial variability, clustering-declustering and intermittency, consistent with multifractal scaling. The sequential growth of events during time scale shows multifractal behavior of seismicity in the focal zone. The results indicate that the extensive heterogeneity and time-dependent strength are considered to generate distinct aftershock events. These factors have structural impacts on intraplate seismicity, suggesting multifractal and unstable nature of the Van event. Multifractal seismicity is controlled by complex evolution of crustal-scale faulting, mechanical heterogeneity and seismic deformation anisotropy. Overall seismicity pattern of aftershocks provides the mechanism for strain softening process to explain the principal thrusting event in the Van earthquake. Strain localization with fault weakening controls the seismic characterization of Van earthquake and contributes to explain the anomalous occurrence of aftershocks and intraplate nature of the Van earthquake. 相似文献
8.
Field observations and analog models show that cross-basin faults play a key role in the evolution of pull-apart basins and dominate the distribution of earthquake rupture in basin areas. We studied the long-term history of large earthquakes on a cross-basin fault to reveal its behavior in response to propagating earthquake rupture and gain insight into the evolution of the pull-apart basin. A number of pull-apart basins have developed along the Haiyuan fault in the northeastern Tibetan Plateau, the largest being the Ganyanchi pull-apart basin. The surface rupture associated with the 1920 M 8.5 earthquake shows that a cross-basin fault developed in the basin and that the basin is now going through the late stage of its evolution. We excavated two trenches and drilled four cores across the cross-basin fault in the basin and found abundant evidence of paleoseismic events. Seven events were identified and 14C-dated. The two youngest events are associated with the historical records of 1092 AD and 1920 AD, respectively. The paleoseismic sequence shows the recurrence of earthquakes characterized by earthquake clusters alternating with a single event. Comparing these with previous paleoseismic results, all the major earthquake events seem to be associated with cascade events that ruptured multi-fault segments, suggesting that only an earthquake of this scale (likely M > 8) can produce obvious surface rupture along the cross-basin fault. We propose that the fault has a long tectonic history, with a series of cascade rupture events that could play an important part in the evolution of the pull-apart basin. 相似文献
9.
The November 27, 2005 Qeshm Island earthquake (Mw 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 (MW?=?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 (MW?=?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. 相似文献
10.
A. Deif Azza Abed Kamal Abdel-Rahman Enayat Abdel Moneim 《Arabian Journal of Geosciences》2011,4(5-6):855-861
Recent and paleo seismicity indicate that moderate seismic activity is relatively large for Aswan area. This is a warning on the possibility of occurrence of earthquakes in the future too. No strong motion records are available in Aswan area for engineers to rely upon. Consequently, the seismological modeling is an alternative approach till sufficient instrumental records around Aswan become available. In the present study, we have developed new ground motion attenuation relationship for events spanning 4.0?≤? M w?≤?7.0 and distance to the surface projection of the fault up to 100 km for Aswan based on a statistically simulated seismological model. We generated suites of ground motion time histories using stochastic technique. The ground motion attenuation relation describes the dependence of the strength of the ground motions on the earthquake magnitude and distance from the earthquake. The proposed equation for peak ground acceleration (PGA) for the bed rock is in the form of: $ {\mathbf{log}}{\text{ }}\left( {{\mathbf{PGA}}/{\mathbf{gal}}} \right){\text{ }} = {\mathbf{1}}.{\mathbf{24}} + {\mathbf{0}}.{\mathbf{358}}{M_{\mathbf{w}}} - {\text{ }}{\mathbf{log}}\left( {\mathbf{R}} \right){\text{ }}-{\text{ }}{\mathbf{0}}.{\mathbf{008}}{\text{ }}{\mathbf{R}}{\text{ }} + {\text{ }}{\mathbf{0}}.{\mathbf{22}}{\text{ }}{\mathbf{P}} $ . Where PGA is the peak ground acceleration in gal (cm/s2); Mw, its moment magnitude; R is the closest distance between the rupture projection and the site of interest; and the factor P is a dummy variable. It is observed that attenuation of strong motion in Aswan is correlated with those used before in Egypt. 相似文献
11.
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 (Mw???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 (Mw???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. 相似文献
12.
In this study, the seismicity rate changes that can represent an earthquake precursor were investigated along the Sagaing Fault Zone (SFZ), Central Myanmar, using the Z value technique. After statistical improvement of the existing seismicity data (the instrumental earthquake records) by removal of the foreshocks and aftershocks and man-made seismicity changes and standardization of the reported magnitude scales, 3574 earthquake events with a M w ≥ 4.2 reported during 1977–2015 were found to directly represent the seismotectonic activities of the SFZ. To find the characteristic parameters specifically suitable for the SFZ, seven known events of M w ≥ 6.0 earthquakes were recognized and used for retrospective tests. As a result, utilizing the conditions of 25 fixed earthquake events considered (N) and a 2-year time window (T w), a significantly high Z value was found to precede most of the M w ≥ 6.0 earthquakes. Therefore, to evaluate the prospective areas of upcoming earthquakes, these conditions (N = 25 and T w = 2) were applied with the most up-to-date seismicity data of 2010–2015. The results illustrate that the vicinity of Myitkyina and Naypyidaw (Z = 4.2–5.1) cities might be subject to strong or major earthquakes in the future. 相似文献
13.
Tadashi Maruyama Katsutoshi Iemura Takashi Azuma Toshikazu Yoshioka Masaru Sato Riichiro Miyawaki 《Tectonophysics》2007,429(1-2):45-60
The 2004 Mid-Niigata Prefecture earthquake sequence (mainshock magnitude, MJMA 6.8), which occurred in an active fold-and-thrust belt in northern central Japan, generated a small thrust surface rupture (< 20 cm of vertical displacement) along a previously unmapped northern extension of the active Muikamachi–Bonchi–Seien fault zone, on the eastern margin of the epicentral region. To better understand past seismic behavior of the rupture, we conducted a paleoseismic trenching study across the 10-cm-high west-side-up surface rupture at the foot of a pre-existing 1.8-m-high east-facing scarp, which probably resulted from past earthquake(s). A well-defined west-dipping thrust fault zone accompanied by drag folding and displacing the upper Pliocene to lower Pleistocene strata and the unconformably overlying upper Pleistocene (?) to Holocene strata was exposed. The principal fault zone is connected directly to the 2004 surface rupture. From the deformational characteristics of the strata and radiocarbon dating, we inferred that two large paleoseismic events occurred during the past 9000 years prior to the 2004 event. These two pre-2004 events have a nearly identical fault slip (at minimum, 1.5 m), which is ≥ 15 times that of the 2004 event (∼ 10 cm). These paleoseismic data, coupled with the geological and geomorphological features, suggest that the 2004 event represented non-characteristic behavior of the fault, which can potentially generate a more destructive earthquake accompanied by meter-scale surface displacement. This study provides insight into the interpretation of past faulting events and increases our understanding of rupture behavior. 相似文献
14.
A. K. Abdel-Fattah A. M. Al-Amri M. S. Fnais kamal Abdelrahman 《Arabian Journal of Geosciences》2014,7(8):3325-3337
On 19 May 2009, an earthquake sequence of M w?=?4.8 occurred at 25.20°N 37.76°E about 60 km onshore of the Red Sea coastline, Saudi Arabia. In the present study, the digital waveform data from the largest four events were used to estimate the source parameters and attenuation characteristics along the source-to-station path in the Arabian Shield. A grid search technique, combined with an assumption of circular source model, was applied to find the best-fit spectral amplitude over the space parameters: long period spectral level (Ω 0), corner frequency (f 0) and asymptotic high-frequency fall-off (γ). Consequently, the spectral parameters were used to estimate source parameters: seismic moment, fault radius (assumed circular rupture model) and stress drop. Seismic moments are founded to be within the range of 2.34E+14 to 2.83E+16 Nm and their corresponding moment magnitudes range from 3.5 to 4.8; the fault radius ranges from 369 to 1,498 m, and stress drops are observed in the range of 8.7 to 32.0 b. The spectral slopes beyond the corner frequency displayed ω ?2.4 to ω ?2.6 behaviours in contrast with Brune's source model of ω ?2. This finding requires more detailed investigations on large data sets to distinguish the behaviour mechanism of the spectral slopes at high frequencies. By taking the ratio between observed and calculated spectra, the attenuation curves for P and S waves were derived along the source-to-station paths. The preliminarily results exhibited high quality factors of Q α?=?3,883 and Q β?=?3,530 for P and S waves, respectively. To this end, the ratio Q β/Q α is founded to be slightly less than unity indicating that the body waves from source-to-station paths crossed a crustal volume that is partially saturated with fluids causing lower attenuation effect on P waves than on S waves in the Arabian Shield. 相似文献
15.
During the 1st decade of the 21st century, the study area of Talala, Saurashtra of western India witnessed three damaging earthquakes of moderate magnitude, year 2007 [Mw 5.0; Mw 4.8] and in the year 2011 [Mw 5.1] that generated public panic in the region. The last damaging moderate earthquake of the 20th October 2011 in Talala region (21.09°N;70.45°E), located at about 200 km south to the devastating 2001 Bhuj (23.412°N, 70.232°E) mainshock (Mw 7.6), jolted the entire Saurashtra region of Gujarat. A long series of aftershocks followed hereafter, recorded at nine seismograph/accelerograph stations. Hypocenters of aftershocks were relocated accurately using absolute and relative travel time (double-difference) method. In this study, we, for the first time, determined 3-D tomographic images of the upper crust beneath the 2011 Talala earthquake source zone by inverting about 1135 P and 1125 S wave arrival time data. Estimates of seismic velocities (Vp, Vs) and Poisson’s ratio (σ) structures offer a reliable interpretation of crustal heterogeneities and their bearing on geneses of moderate earthquakes and their aftershock sequences beneath the source zone. It is found that the 2011 Talala mainshock hypocenter depth (6 km) is located near the boundary of the low and high velocity (Vp, Vs) and the source zone is associated with low-σ anomalies guarded by the prominent high-σ anomalies along the active fault zone having strike-slip motion beneath the earthquake source zone. The pattern of distribution of (Vp, Vs, σ) and its association with occurrences of aftershocks provide seismological evidence for the neo-tectonics in the region having left lateral strike-slip motion of the fault. 相似文献
16.
Tobias Diehl John Clinton Nicolas Deichmann Carlo Cauzzi Philipp Kästli Toni Kraft Irene Molinari Maren Böse Clotaire Michel Manuel Hobiger Florian Haslinger Donat Fäh Stefan Wiemer 《Swiss Journal of Geoscience》2018,111(1-2):221-244
This report summarizes the seismicity in Switzerland and surrounding regions in the years 2015 and 2016. In 2015, the Swiss Seismological Service detected and located 735 earthquakes in the region under consideration. With a total of 20 earthquakes of magnitude ML ≥ 2.5, the seismic activity of potentially felt events in 2015 was close to the average of 23 earthquakes over the previous 40 years. Seismic activity was above average in 2016 with 872 located earthquakes of which 31 events had ML ≥ 2.5. The strongest event in the analyzed period was the ML 4.1 Salgesch earthquake, which occurred northeast of Sierre (VS) in October 2016. The event was felt in large parts of Switzerland and had a maximum intensity of V. Derived focal mechanisms and relative hypocenter relocations of aftershocks image a SSE dipping reverse fault, which likely also hosted an ML 3.9 earthquake in 2003. Another remarkable earthquake sequence in the Valais occurred close to Sion with four felt events (ML 2.7–3.2) in 2015/16. We associate this sequence with a system of WNW-ESE striking fault segments north of the Rhône valley. Similarities with a sequence in 2011, which was located about 10 km to the NE, suggest the existence of an en-echelon system of basement faults accommodating dextral slip along the Rhône-Simplon line in this area. Another exceptional earthquake sequence occurred close to Singen (Germany) in November 2016. Relocated hypocenters and focal mechanisms image a SW dipping transtensional fault segment, which is likely associated with a branch of the Hegau-Bodensee Graben. On the western boundary of this graben, micro-earthquakes close to Schlattingen (TG) in 2015/16 are possibly related to a NE dipping branch of the Neuhausen Fault. Other cases of earthquakes felt by the public during 2015/16 include earthquakes in the region of Biel, Vallorcine, Solothurn, and Savognin. 相似文献
17.
R.B.S. Yadav E.E. Papadimitriou V.G. Karakostas D. Shanker B.K. Rastogi S. Chopra A.P. Singh Santosh Kumar 《Journal of Asian Earth Sciences》2011,40(1):303-314
A damaging and widely felt moderate (Mw 5.0) earthquake occurred in the Talala region of Saurashtra, Gujarat (western India) on November 6, 2007. The highly productive sequence comprised about 1300 micro earthquakes (M > 0.5) out of which 325 of M ? 1.5 that occurred during November 6, 2007–January 10, 2008 were precisely located. The spatial aftershock distribution revealed a NE–SW striking fault in accordance with the centroid moment tensor solution, which in turn implies left-lateral motion. The orientation and sense of shear are consistent with similarly orientated geological fault identified in the area from satellite imagery and field investigation.The aftershocks temporal decay, b-value of frequency–magnitude distribution, spatial fractal dimension, D, and slip ratio (ratio of the slip occurred on the primary fault to the total slip) were examined with the purpose to identify the properties of the sequence. The high b-value (1.18 ± 0.01) may be attributed to the paucity of the larger (M ? 4.0) aftershocks and reveals crustal heterogeneity and low stress regime. The high p-value (1.10 ± 0.39), implying fast decay rate of aftershocks, evidences high surface heat flux. A value of the spatial fractal dimension (D) equal to 2.21 ± 0.02 indicates random spatial distribution and source in a two-dimensional plane that is being filled-up by fractures. A slip ratio of 0.42 reveals that more slip occurred on secondary fault systems.The static Coulomb stress changes due to the coseismic slip of the main shock, enhanced off fault aftershock occurrence. The occurrence of a moderate earthquake (Mw 4.3) on October 5, 2008 inside a region of positive Coulomb stress changes supports the postulation on aftershock triggering. When the stress changes were resolved on a cross section including the stronger (M4.8) foreshock plane that is positioned adjacent to the main fault, it became evident that the activity continued there due to stress transfer from the main rupture. 相似文献
18.
This paper presents the computation of time series of the 22 July 2007 M 4.9 Kharsali earthquake. It occurred close to the Main Central Thrust (MCT) where seismic gap exists. The main shock and
17 aftershocks were located by closely spaced eleven seismograph stations in a network that involved VSAT based real-time
seismic monitoring. The largest aftershock of M 3.5 and other aftershocks occurred within a small volume of 4 × 4 km horizontal extent and between depths of 10 and 14 km.
The values of seismic moment (M
∘) determined using P-wave spectra and Brune’s model based on f
2 spectral shape ranges from 1018 to 1023 dyne-cm. The initial aftershocks occurred at greater depth compared to the later aftershocks. The time series of ground motion
have been computed for recording sites using geometric ray theory and Green’s function approach. The method for computing
time series consists in integrating the far-field contributions of Green’s function for a number of distributed point source.
The generated waveforms have been compared with the observed ones. It has been inferred that the Kharsali earthquake occurred
due to a northerly dipping low angle thrust fault at a depth of 14 km taking strike N279°E, dip 14° and rake 117°. There are
two regions on the fault surface which have larger slip amplitudes (asperities) and the rupture which has been considered
as circular in nature initiated from the asperity at a greater depth shifting gradually upwards. The two asperities cover
only 10% of the total area of the causative fault plane. However, detailed seismic imaging of these two asperities can be
corroborated with structural heterogeneities associated with causative fault to understand how seismogenesis is influenced
by strong or weak structural barriers in the region. 相似文献
19.
Statistical analysis of landslides caused by the Mw 6.9 Yushu,China, earthquake of April 14, 2010 总被引：5，自引：0，他引：5
The April 14, 2010 Yushu, China, earthquake (Mw 6.9) triggered a great number of landslides. At least 2,036 co-seismic landslides, with a total coverage area of 1.194 km2, were delineated by visual interpretation of aerial photographs and satellite images taken following the earthquake, and verified by field inspection. Based on the mapping results, a statistical analysis of the spatial distribution of these landslides is performed using the landslide area percentage (LAP), defined as the percentage of the area affected by the landslides, and landslide number density (LND), defined as the number of landslides per square kilometer. The purpose is to clarify how the landslides correlate the control factors, which are the elevation, slope angle, slope aspect, slope position, distance from drainages, lithology, distance from the surface rupture, and peak ground acceleration (PGA). The results show that both LAP and LND have strongly positive correlations with slope angle and negative correlations with distance from the surface rupture and distance from drainages. The highest LAP and LPD values are in places of elevations from 3,800 to 4,000 m. The slopes producing landslides are mostly facing toward NE, E, and SE. The geological units of Q4 al-pl, N, and T3 kn 1 have the highest concentrations of co-seismic landslides. No apparent correlations are present between LAP and LND values and PGA. On both sides of the surface rupture, the landslide distributions are almost similar except a few exceptions, likely associated with the nature of the strike-slip seismogenic fault for this event. The bivariate statistical analysis shows that, in descending order, the earthquake-triggered landslide impact factors are distance from surface rupture > slope angle > distance from drainages > lithology > PGA. Besides, as the detailed co-seismic landslides inventories related to strike-slip earthquakes are still few compared with that of thrusting-fault earthquakes, this case study would shed new light on the subject. For instance, the landslide spatial distribution on both sides of the strike-slip seismogenic fault is rather different from that of thrusting-fault earthquakes. It reminds us to take different strategies of measures for prevention and mitigation of landslides induced by earthquakes with different mechanisms. 相似文献
20.
In 2001, a special issue of the Bulletin of the Seismological Society of America (BSSA) featured seismological research for the 1999 Chi–Chi Taiwan earthquake. This study uses source parameters suggested by the first author in this special issue to estimate static stress drop associated with the Chi–Chi earthquake. The waveform simulation method was used to carefully examine these source parameters. The simulation results indicate that source parameters, inferred from near-fault observations, are well determined. According to the rupture area and slip, the static stress drops (Δσs) obtained were distributed between a small value of 47 bars near the epicentral region and a much larger value (>200 bars) to the north. Similar trends in dynamic stress drop (Δσd) were also recognized by the first author in his paper published in 2001 BSSA special issue. Comparing the Δσs with Δσd, satisfies the relation Δσs/Δσd ≈ 1. This relation suggests that fault motion is mostly spent releasing seismic wave energy during the rupture process of the Chi–Chi earthquake. The consistency between static and dynamic stress drops thus provides a measure of energy-moment (Es/M0) ratios, which range from 9.0 × 10−5 to 6.5 × 10−4. The average Es/M0 ratio estimated for the northern portions of the fault is 3.4 × 10−4, which is about 3 times that of the south. Such a high Es/M0 ratio can be interpreted as having low strength in the rupture for the northern portions of the fault, where the fault would release less energy per unit rupture surface to create the new rupture. 相似文献