The new GPS data can map crustal strain rates over large areas with a useful degree of precision. Stable strain measurement results open the door for improved estimates of earthquake occurrence. The Kostrov’s formula...The new GPS data can map crustal strain rates over large areas with a useful degree of precision. Stable strain measurement results open the door for improved estimates of earthquake occurrence. The Kostrov’s formula (1974) translates the smoothed strain rates in North China into geodetic moment rates. In North China, the ratio of seismic moment released to moment accumulated from GPS measurement is 60.6% in NS direction, 68.9% in EW direction, and 104.1% in NE shear direction. The near unit ratio points to the reliability of GPS measurements there. The combination of historical seismicity and GPS measurement offers a powerful attack on earthquake hazard.展开更多
The goal of this study is to determine earthquake source processes of moderate to strong earthquakes in Western China using data recorded by the digital broadband stations in and near China. There are 12 broadband sta...The goal of this study is to determine earthquake source processes of moderate to strong earthquakes in Western China using data recorded by the digital broadband stations in and near China. There are 12 broadband stations on the Chinese mainland. This paper used a kind of moment tensor inversion method to study the large earthquakes in the Xizang (Tibet) region of China.In this study, we first ported and tested a moment\|tensor inversion code and then applied the technique to a large (magnitude M s=7.9) earthquake in Xizang region of China. The inversion for the earthquake moment tensor is performed in the frequency domain by fitting long\|period observed spectra to synthetic spectra calculated. For details of the method refer to Giardini and Beranzoli (1992). As part of the project, we extended the library of synthetics by including local (>100km) and teleseismic distances (2000km<distance<9000km) which allows now the use of data from additional stations. The Xizang region is one of the most unusual and spectacular topographic features on Earth rising, on average, more than 4000 meters above sea level. The high topography is the result of the collision between the Indian and Asian tectonic plates which is also the cause for the area’s high seismicity rate. As a preliminary study, the moment tensors were obtained for the large earthquake ( M s=7.9) of 8 Nov 1997 in Xizang region using data from five stations. The result is similar to the Harvard CMT solution; for strike, dip and rake, this paper obtained 343, 76 and -177 degrees, respectively, while the Harvard CMT values are 348, 88 and 159. The moment magnitude estimate of Harvard is only 0.1 unit larger than my estimate of M w=7 4.. The fit in the frequency domain (phase and amplitude) suggests the reasonable result. At long periods the earthquake depth is generally not well resolved. Inversions for several trial depths, however, show a clear variance minimum for centroid depths (the average depth over the entire rupture plane) of a little less than about 12km. This is roughly consistent with the Harvard estimate of 16.4km. The fit result also shows that the fault plane solution is stable and well resolved. The test of the frequence band influence suggests that for each band the results are stable over a wide depth range. However, the results at one trial depth slightly depend on the frequency band. This research is being performed still, due to the important implication of Xizang region on geodynamics studies. Combining with more data, geological investigation and stress field analysis, we will give further results and discussion.展开更多
plane with the strike of 127°, the dip of 79° and the rake of 171°. The rupture process inversion result of MS=7.9 earthquake shows that the total rupture duration is about 37 s, the scalar moment tenso...plane with the strike of 127°, the dip of 79° and the rake of 171°. The rupture process inversion result of MS=7.9 earthquake shows that the total rupture duration is about 37 s, the scalar moment tensor is M0=0.97 × 1020 N·m. Rupture mainly occurred on the shallow area with 110 km long and 30 km wide, the location in which the rupture initiated is not where the main rupture took place, and the area with slip greater than 0.5 m basically lies within 35 km deep middle-crust under the earth surface. The maximum static slip is 3.6 m. There are two distinct areas with slip larger than 2.0 m. We noticed that when the rupture propagated towards northwest and closed to the area around the MS=7.3 hypocenter, the slip decreased rapidly, which may indicate that the rupture process was stopped by barriers. The consistence of spatial distribution of slip on the fault plane with the distribution of aftershocks also supports that the rupture is a heterogeneous process owing to the presence of barriers.展开更多
Distribution of apparent stress in Chinese mainland and its surrounding regions was presented using the NEIC broadband radiated energy catalogue and the Harvard CMT catalogue from January 1987 to December 1998. Due to...Distribution of apparent stress in Chinese mainland and its surrounding regions was presented using the NEIC broadband radiated energy catalogue and the Harvard CMT catalogue from January 1987 to December 1998. Due to the limitation on the number of samples, reliable results are only for the western China. It is observed that the average apparent stress in Chinese mainland is 0.8 MPa; The maximum apparent stress to the east of the Tibetan plateau is 2.6 MPa; And the average apparent stress in the north-south seismic belt is more than one time higher than its adjacent regions. Distribution pattern of apparent stress seems to have a large-scale correlation with the cumulative energy release level in the 20th century.展开更多
In this paper, the method which can combine different seismic data with the different precision and completeness, even the palaeo-earthquake data, has been applied to estimate the yearly seismic moment rate in the sei...In this paper, the method which can combine different seismic data with the different precision and completeness, even the palaeo-earthquake data, has been applied to estimate the yearly seismic moment rate in the seismic region. Based on this, the predictable model of regional time-magnitude has been used in North China and Southwest China. The normal correlation between the time interval of the events and the magnitude of the last strong earthquake shows that the model is suitable. The value of the parameter c is less than the average value of 0.33 that is obtained from the events occurred in the plate boundary in the world. It is explained that the correlativity between the recurrence interval of the earthquake and the magnitude of the last strong event is not obvious. It is shown that the continental earthquakes in China are different from that occurred in the plate boundary and the recurrence model for the continental events are different from the one for the plate boundary events. Finally the seismic risk analysis based on this model for North China and Southwest China is given in this paper.展开更多
文摘The new GPS data can map crustal strain rates over large areas with a useful degree of precision. Stable strain measurement results open the door for improved estimates of earthquake occurrence. The Kostrov’s formula (1974) translates the smoothed strain rates in North China into geodetic moment rates. In North China, the ratio of seismic moment released to moment accumulated from GPS measurement is 60.6% in NS direction, 68.9% in EW direction, and 104.1% in NE shear direction. The near unit ratio points to the reliability of GPS measurements there. The combination of historical seismicity and GPS measurement offers a powerful attack on earthquake hazard.
文摘The goal of this study is to determine earthquake source processes of moderate to strong earthquakes in Western China using data recorded by the digital broadband stations in and near China. There are 12 broadband stations on the Chinese mainland. This paper used a kind of moment tensor inversion method to study the large earthquakes in the Xizang (Tibet) region of China.In this study, we first ported and tested a moment\|tensor inversion code and then applied the technique to a large (magnitude M s=7.9) earthquake in Xizang region of China. The inversion for the earthquake moment tensor is performed in the frequency domain by fitting long\|period observed spectra to synthetic spectra calculated. For details of the method refer to Giardini and Beranzoli (1992). As part of the project, we extended the library of synthetics by including local (>100km) and teleseismic distances (2000km<distance<9000km) which allows now the use of data from additional stations. The Xizang region is one of the most unusual and spectacular topographic features on Earth rising, on average, more than 4000 meters above sea level. The high topography is the result of the collision between the Indian and Asian tectonic plates which is also the cause for the area’s high seismicity rate. As a preliminary study, the moment tensors were obtained for the large earthquake ( M s=7.9) of 8 Nov 1997 in Xizang region using data from five stations. The result is similar to the Harvard CMT solution; for strike, dip and rake, this paper obtained 343, 76 and -177 degrees, respectively, while the Harvard CMT values are 348, 88 and 159. The moment magnitude estimate of Harvard is only 0.1 unit larger than my estimate of M w=7 4.. The fit in the frequency domain (phase and amplitude) suggests the reasonable result. At long periods the earthquake depth is generally not well resolved. Inversions for several trial depths, however, show a clear variance minimum for centroid depths (the average depth over the entire rupture plane) of a little less than about 12km. This is roughly consistent with the Harvard estimate of 16.4km. The fit result also shows that the fault plane solution is stable and well resolved. The test of the frequence band influence suggests that for each band the results are stable over a wide depth range. However, the results at one trial depth slightly depend on the frequency band. This research is being performed still, due to the important implication of Xizang region on geodynamics studies. Combining with more data, geological investigation and stress field analysis, we will give further results and discussion.
基金The Specialized Funds for National Key Basic Study (G1998040704), the Dual Project of China Earthquake Admini-stration (9691309020301) and National Natural Science Foundation of China (46764010).
文摘plane with the strike of 127°, the dip of 79° and the rake of 171°. The rupture process inversion result of MS=7.9 earthquake shows that the total rupture duration is about 37 s, the scalar moment tensor is M0=0.97 × 1020 N·m. Rupture mainly occurred on the shallow area with 110 km long and 30 km wide, the location in which the rupture initiated is not where the main rupture took place, and the area with slip greater than 0.5 m basically lies within 35 km deep middle-crust under the earth surface. The maximum static slip is 3.6 m. There are two distinct areas with slip larger than 2.0 m. We noticed that when the rupture propagated towards northwest and closed to the area around the MS=7.3 hypocenter, the slip decreased rapidly, which may indicate that the rupture process was stopped by barriers. The consistence of spatial distribution of slip on the fault plane with the distribution of aftershocks also supports that the rupture is a heterogeneous process owing to the presence of barriers.
基金The MOST under contract number G1998040705 95-S-05 and 2001BA601B02.
文摘Distribution of apparent stress in Chinese mainland and its surrounding regions was presented using the NEIC broadband radiated energy catalogue and the Harvard CMT catalogue from January 1987 to December 1998. Due to the limitation on the number of samples, reliable results are only for the western China. It is observed that the average apparent stress in Chinese mainland is 0.8 MPa; The maximum apparent stress to the east of the Tibetan plateau is 2.6 MPa; And the average apparent stress in the north-south seismic belt is more than one time higher than its adjacent regions. Distribution pattern of apparent stress seems to have a large-scale correlation with the cumulative energy release level in the 20th century.
文摘In this paper, the method which can combine different seismic data with the different precision and completeness, even the palaeo-earthquake data, has been applied to estimate the yearly seismic moment rate in the seismic region. Based on this, the predictable model of regional time-magnitude has been used in North China and Southwest China. The normal correlation between the time interval of the events and the magnitude of the last strong earthquake shows that the model is suitable. The value of the parameter c is less than the average value of 0.33 that is obtained from the events occurred in the plate boundary in the world. It is explained that the correlativity between the recurrence interval of the earthquake and the magnitude of the last strong event is not obvious. It is shown that the continental earthquakes in China are different from that occurred in the plate boundary and the recurrence model for the continental events are different from the one for the plate boundary events. Finally the seismic risk analysis based on this model for North China and Southwest China is given in this paper.
