Based on Gutenberg-Richter＇s relation,Bath＇s law,Omori＇s law and Well＇s relation of rupture scale,this paper forecasts the temporal decay,total number,possible area and greatest magnitude of strong aftershocks（gr...Based on Gutenberg-Richter＇s relation,Bath＇s law,Omori＇s law and Well＇s relation of rupture scale,this paper forecasts the temporal decay,total number,possible area and greatest magnitude of strong aftershocks（greater than or equal to M6.0） of the MS8.0 Wenchuan earthquake by using the magnitude and statistical parameters of earthquakes in California area of USA.The number of strong aftershocks,the parameters of Gutenberg-Richter＇s relation and the modified form of Omori＇s law are validated based on the relocation data of aftershock sequence of the MS8.0 Wenchuan earthquake.Moreover,the spatio-temporal characteristics and wave energy release of the strong aftershocks（M≥6.0） are analyzed.The result shows that strong aftershocks may occur at the end of local drop and sharp drop on the wave energy release curve.展开更多
By calculating the azimuth, phase angle and change rate of tidal force, and contrasting their rupture types, we find that in 6 of 11 reverse faulting earthquakes, the angles between the direction of the horizontal tid...By calculating the azimuth, phase angle and change rate of tidal force, and contrasting their rupture types, we find that in 6 of 11 reverse faulting earthquakes, the angles between the direction of the horizontal tidal force and compressive principal stress are within 33°, the vertical phase angles of all 8 strike-slip earthquakes are in the upward peak section and the vertical phase angles of two extensional normal faulting earthquakes are in the downward peak section. According to the above statistics, the mechanism of tidal force triggering of the Wenchnan Ms8. 0 Earthquake and its strong aftershocks is discussed.展开更多
The M8.0 Wenchuan earthquake occurred on the Longmenshan fault zone. Based on field investigation of the surface rupture and focal mechanism study of the aftershocks, we discuss the geological relationship of the main...The M8.0 Wenchuan earthquake occurred on the Longmenshan fault zone. Based on field investigation of the surface rupture and focal mechanism study of the aftershocks, we discuss the geological relationship of the main, secondary and triggered ruptures. The main rupture is about 200km long and can be divided into the south part and the north part. The south part consists of two parallel fault zones characterized by reverse faulting, with several parallel secondary ruptures on the hanging wall of the main fault, and the north part is a single main fault zone characterized by lateral strike-slip and reverse faulting. Compared to a 300km long aftershock distribution, the surface rupture only occupies 200km, and the remaining lOOkm on the northeast of the main rupture was triggered by aftershocks. Study on the ruptures of this earthquake will be useful for studying the earthquake risk evolution on the Longmenshan fault system.展开更多
Records of the May 12, 2008 Ms8.0 Wenchuan, Sichuan, earthquake from 27 stations of Shaanxi Digital Strong Motion Network are processed and analyzed, including baseline adjustment of acceleration traces, filtering, an...Records of the May 12, 2008 Ms8.0 Wenchuan, Sichuan, earthquake from 27 stations of Shaanxi Digital Strong Motion Network are processed and analyzed, including baseline adjustment of acceleration traces, filtering, and calculations of velocities, displacements and acceleration response spectra. The results show that direction energy radiation of the large earthquake and horizontal inhomogeneous medium along the wave traveling path might both have some effect on the scattering degree of the attenuation of PGAH, besides influence of local site conditions. For the same intensity, the ratios of PGA/PGV are commonly small, on average about 5, which indicates that long period components are rich in ground motion. Intensities for most sites of the stations are within V -VII. The larger one among PGAE-W and PGAN-S is quite close to their PGAH, which is less than 10 % in relative deviation. The dominated waves are surface waves. The thicker the soil overburden is, the stronger the surface wave will be and the longer the shaking will last. Local site conditions have strong effects on ground motion, especially those of thick sediment filled-in basins, as they can significantly amplify long-period components.展开更多
Based on abundant aftershock sequence data of the Wenchuan Ms8.0 earthquake on May 12, 2008, we studied the spatio-temporal variation process and segmentation rupture characteristic. Dense aftershocks distribute along...Based on abundant aftershock sequence data of the Wenchuan Ms8.0 earthquake on May 12, 2008, we studied the spatio-temporal variation process and segmentation rupture characteristic. Dense aftershocks distribute along Longmenshan central fault zone of NE direction and form a narrow strip with the length of 325 krn and the depth between several and 40 km. The depth profile （section of NW direction） vertical to the strike of aftershock zone （NE direction） shows anisomerous wedgy distribution characteristic of afiershock concentrated regions; it is related to the force form of the Longmenshan nappe tectonic belt. The stronger aftershocks could be divided into northern segment and southern segment apparently and the focal depths of strong aftershocks in the 50 km area between northern segment and southern segment are shallower. It seems like ＇to be going to rupture＇ segment. We also study focal mechanisms and segmentation of strong aftershocks. The principal compressive stress azimuth of aftershock area is WNW direction and the faulting types of aftershocks at southern and northern segment have the same proportion. Because afiershocks distribute on different secondary faults, their focal mechanisms present complex local tectonic stress field. The faulting of seven strong earthquakes on the Longmenshan central fault is mainly characterized by thrust with the component of right-lateral strike-slip. Meantime six strong aftershocks on the Longmenshan back-range fault and Qingchuan fault present strike-slip faulting. At last we discuss the complex segmentation rupture mechanism of the Wenchuan earthquake.展开更多
The aftershock activity of the May 12, 2008 Wenchuan Ms8.0 Earthquake Sequence shows an obvious segmented feature. Most of the large aftershocks were distributed in the north and south parts of the aftershock zone. Th...The aftershock activity of the May 12, 2008 Wenchuan Ms8.0 Earthquake Sequence shows an obvious segmented feature. Most of the large aftershocks were distributed in the north and south parts of the aftershock zone. Thrusting was dominant with a small amount of strike-slip component in the south part. The aftershock activity decayed gradually, presenting the sequence features of a mainshock-aftershock pattern. The north part was the ending area of the malnshock fracture where strike-slipping was dominant, showing an obvious swarm feature. Therefore it became the major area for large aftershocks. The modulation of the earth tide on aftershock activity is remarkable; most large aftershocks occur during the period of flood and neap tide. The time period around 16：00 was the dominant occurring time for large aftershocks. The p-value, a parameter of modified Omori formula, increases gradually with time, and reaches about 1 at the end. Based on previous study, the sequence patterns, magnitude of maximum aftershock, as well as the duration of aftershock activity has been discussed. The primary results also show that the magnitude difference between the maiushock and the maximum aftershock is proportional to the rupture size of the maiushock for huge earthquakes of about Ms8.0. This means that when the magnitudes of the earthquakes are nearly the same, large rupture size corresponds to sufficient energy release.展开更多
Local site conditions play an important role in the effective application of strong motion recordings.In the China National Strong Motion Observation Network System（NSMONS）,some of the stations do not provide boreho...Local site conditions play an important role in the effective application of strong motion recordings.In the China National Strong Motion Observation Network System（NSMONS）,some of the stations do not provide borehole information,and correspondingly,do not assign the site classes yet.In this paper,site classification methodologies for free-field strong motion stations are reviewed and the limitations and uncertainties of the horizontal-to-vertical spectral ratio（HVSR） methods are discussed.Then,a new method for site classification based on the entropy weight theory is proposed.The proposed method avoids the head or tail joggle phenomenon by providing the objective and subjective weights.The method was applied to aftershock recordings from the 2008 Wenchuan earthquake,and 54 free-field NSMONS stations were selected for site classification and the mean HVSRs were calculated.The results show that the improved HVSR method proposed in this paper has a higher success rate and could be adopted in NSMONS.展开更多
Sliding-window cross-correlation method is firstly adopted to identify sPn phase, and to constrain focal depth from regional seismograms, by measuring the time separation between sPn and Pn phases. We present the foca...Sliding-window cross-correlation method is firstly adopted to identify sPn phase, and to constrain focal depth from regional seismograms, by measuring the time separation between sPn and Pn phases. We present the focal depths of the 17 moderate-sized aftershocks (MS≥5.0) of the Wenchuan MS8.0 earth-quake, using the data recorded by the regional seismic broadband networks of Shaanxi, Qinghai, Gansu, Yunnan and Sichuan. Our results show focal depths of aftershocks range from 8 to 20 km, and tend to cluster at two average depths, separate at 32.5°N, i.e., 11 km to the south and 17 km to the north, indicating that these aftershocks are origin of upper-to-middle crust. Combined with other results, we suggest that the Longmenshan fault is not a through-going crustal fault and the Pingwu-Qingchuan fault may be not the northward extension of the Longmenshan thrust fault.展开更多
基金supported by Basic Science and Research Fund for Chinese Commonweal Institutes under grant No. 2008B07the National Natural Science Foundation of China under grant No. 90715042+1 种基金Special Research Project of Earth-quake Engineering under grant No. 200808008National Science and Technology Support Plan under grant No. 2006BAC13B02
文摘Based on Gutenberg-Richter＇s relation,Bath＇s law,Omori＇s law and Well＇s relation of rupture scale,this paper forecasts the temporal decay,total number,possible area and greatest magnitude of strong aftershocks（greater than or equal to M6.0） of the MS8.0 Wenchuan earthquake by using the magnitude and statistical parameters of earthquakes in California area of USA.The number of strong aftershocks,the parameters of Gutenberg-Richter＇s relation and the modified form of Omori＇s law are validated based on the relocation data of aftershock sequence of the MS8.0 Wenchuan earthquake.Moreover,the spatio-temporal characteristics and wave energy release of the strong aftershocks（M≥6.0） are analyzed.The result shows that strong aftershocks may occur at the end of local drop and sharp drop on the wave energy release curve.
基金sponsored under the Seismic Situation Tracing Directional Work Project in Contract System in 2009 (20090203012009010107),China
文摘By calculating the azimuth, phase angle and change rate of tidal force, and contrasting their rupture types, we find that in 6 of 11 reverse faulting earthquakes, the angles between the direction of the horizontal tidal force and compressive principal stress are within 33°, the vertical phase angles of all 8 strike-slip earthquakes are in the upward peak section and the vertical phase angles of two extensional normal faulting earthquakes are in the downward peak section. According to the above statistics, the mechanism of tidal force triggering of the Wenchnan Ms8. 0 Earthquake and its strong aftershocks is discussed.
基金sponsored by the Special Earthquake Research Program(20070851)National Key Basic Research Development Planning grogram(2004CB418401)+1 种基金Basic Science Research Professional of Institute of Crustal Dynamics (2008)National Science and Technology Support Program(2006BAC13B01 -0202),China
文摘The M8.0 Wenchuan earthquake occurred on the Longmenshan fault zone. Based on field investigation of the surface rupture and focal mechanism study of the aftershocks, we discuss the geological relationship of the main, secondary and triggered ruptures. The main rupture is about 200km long and can be divided into the south part and the north part. The south part consists of two parallel fault zones characterized by reverse faulting, with several parallel secondary ruptures on the hanging wall of the main fault, and the north part is a single main fault zone characterized by lateral strike-slip and reverse faulting. Compared to a 300km long aftershock distribution, the surface rupture only occupies 200km, and the remaining lOOkm on the northeast of the main rupture was triggered by aftershocks. Study on the ruptures of this earthquake will be useful for studying the earthquake risk evolution on the Longmenshan fault system.
文摘Records of the May 12, 2008 Ms8.0 Wenchuan, Sichuan, earthquake from 27 stations of Shaanxi Digital Strong Motion Network are processed and analyzed, including baseline adjustment of acceleration traces, filtering, and calculations of velocities, displacements and acceleration response spectra. The results show that direction energy radiation of the large earthquake and horizontal inhomogeneous medium along the wave traveling path might both have some effect on the scattering degree of the attenuation of PGAH, besides influence of local site conditions. For the same intensity, the ratios of PGA/PGV are commonly small, on average about 5, which indicates that long period components are rich in ground motion. Intensities for most sites of the stations are within V -VII. The larger one among PGAE-W and PGAN-S is quite close to their PGAH, which is less than 10 % in relative deviation. The dominated waves are surface waves. The thicker the soil overburden is, the stronger the surface wave will be and the longer the shaking will last. Local site conditions have strong effects on ground motion, especially those of thick sediment filled-in basins, as they can significantly amplify long-period components.
基金supported by National Key Basic Research 973bNational Scientific Technology Support Plan (2006BAC01B02-01-01).
文摘Based on abundant aftershock sequence data of the Wenchuan Ms8.0 earthquake on May 12, 2008, we studied the spatio-temporal variation process and segmentation rupture characteristic. Dense aftershocks distribute along Longmenshan central fault zone of NE direction and form a narrow strip with the length of 325 krn and the depth between several and 40 km. The depth profile （section of NW direction） vertical to the strike of aftershock zone （NE direction） shows anisomerous wedgy distribution characteristic of afiershock concentrated regions; it is related to the force form of the Longmenshan nappe tectonic belt. The stronger aftershocks could be divided into northern segment and southern segment apparently and the focal depths of strong aftershocks in the 50 km area between northern segment and southern segment are shallower. It seems like ＇to be going to rupture＇ segment. We also study focal mechanisms and segmentation of strong aftershocks. The principal compressive stress azimuth of aftershock area is WNW direction and the faulting types of aftershocks at southern and northern segment have the same proportion. Because afiershocks distribute on different secondary faults, their focal mechanisms present complex local tectonic stress field. The faulting of seven strong earthquakes on the Longmenshan central fault is mainly characterized by thrust with the component of right-lateral strike-slip. Meantime six strong aftershocks on the Longmenshan back-range fault and Qingchuan fault present strike-slip faulting. At last we discuss the complex segmentation rupture mechanism of the Wenchuan earthquake.
基金sponsored jointly by the Earthquake Scientific Research Program(200708020)the State Scientific and Technologic Support Programof the tenth"Five-Year Plan"(200704032006BAC01B030202)
文摘The aftershock activity of the May 12, 2008 Wenchuan Ms8.0 Earthquake Sequence shows an obvious segmented feature. Most of the large aftershocks were distributed in the north and south parts of the aftershock zone. Thrusting was dominant with a small amount of strike-slip component in the south part. The aftershock activity decayed gradually, presenting the sequence features of a mainshock-aftershock pattern. The north part was the ending area of the malnshock fracture where strike-slipping was dominant, showing an obvious swarm feature. Therefore it became the major area for large aftershocks. The modulation of the earth tide on aftershock activity is remarkable; most large aftershocks occur during the period of flood and neap tide. The time period around 16：00 was the dominant occurring time for large aftershocks. The p-value, a parameter of modified Omori formula, increases gradually with time, and reaches about 1 at the end. Based on previous study, the sequence patterns, magnitude of maximum aftershock, as well as the duration of aftershock activity has been discussed. The primary results also show that the magnitude difference between the maiushock and the maximum aftershock is proportional to the rupture size of the maiushock for huge earthquakes of about Ms8.0. This means that when the magnitudes of the earthquakes are nearly the same, large rupture size corresponds to sufficient energy release.
基金National Key Technology R&D Program Under Grant No.2009BAK55B05Nonprofit Industry Research Project of CEA Under Grant No.201108003Science Foundation of Institute of Engineering Mechanics,CEA Under Grant No.2010C01
文摘Local site conditions play an important role in the effective application of strong motion recordings.In the China National Strong Motion Observation Network System（NSMONS）,some of the stations do not provide borehole information,and correspondingly,do not assign the site classes yet.In this paper,site classification methodologies for free-field strong motion stations are reviewed and the limitations and uncertainties of the horizontal-to-vertical spectral ratio（HVSR） methods are discussed.Then,a new method for site classification based on the entropy weight theory is proposed.The proposed method avoids the head or tail joggle phenomenon by providing the objective and subjective weights.The method was applied to aftershock recordings from the 2008 Wenchuan earthquake,and 54 free-field NSMONS stations were selected for site classification and the mean HVSRs were calculated.The results show that the improved HVSR method proposed in this paper has a higher success rate and could be adopted in NSMONS.
基金the National Natural Science Foundation of China (Grant Nos. 40604009 and 40574040)Special Project for the Fundamental R & D of Institute of Geophysics, China Earthquake Administration (Grant No.DQJB08B20)
文摘Sliding-window cross-correlation method is firstly adopted to identify sPn phase, and to constrain focal depth from regional seismograms, by measuring the time separation between sPn and Pn phases. We present the focal depths of the 17 moderate-sized aftershocks (MS≥5.0) of the Wenchuan MS8.0 earth-quake, using the data recorded by the regional seismic broadband networks of Shaanxi, Qinghai, Gansu, Yunnan and Sichuan. Our results show focal depths of aftershocks range from 8 to 20 km, and tend to cluster at two average depths, separate at 32.5°N, i.e., 11 km to the south and 17 km to the north, indicating that these aftershocks are origin of upper-to-middle crust. Combined with other results, we suggest that the Longmenshan fault is not a through-going crustal fault and the Pingwu-Qingchuan fault may be not the northward extension of the Longmenshan thrust fault.
