In this paper, three existing source spectral models for stochastic finite-fault modeling of ground motion were reviewed. These three models were used to calculate the far-field received energy at a site from a vertic...In this paper, three existing source spectral models for stochastic finite-fault modeling of ground motion were reviewed. These three models were used to calculate the far-field received energy at a site from a vertical fault and the mean spectral ratio over 15 stations of the Northridge earthquake, and then compared. From the comparison, a necessary measure was observed to maintain the far-field received energy independent of subfault size and avoid overestimation of the long- period spectra/level. Two improvements were made to one of the three models (i.e., the model based on dynamic comer frequency) as follows: (i) a new method to compute the subfault comer frequency was proposed, where the subfault comer frequency is determined based on a basic value calculated from the total seismic moment of the entire fault and an increment depending on the seismic moment assigned to the subfault; and (ii) the difference of the radiation energy from each suhfault was considered into the scaling factor. The improved model was also compared with the unimproved model through the far-field received energy and the mean spectral ratio. The comparison proves that the improved model allows the received energy to be more independent of subfault size than the unimproved model, and decreases the overestimation degree of the long-period spectral amplitude.展开更多
The static comer frequency and dynamic comer frequency in stochastic synthesis of ground motion from fi- nite-fault modeling are introduced, and conceptual disadvantages of the two are discussed in this paper. Further...The static comer frequency and dynamic comer frequency in stochastic synthesis of ground motion from fi- nite-fault modeling are introduced, and conceptual disadvantages of the two are discussed in this paper. Furthermore, the non-uniform radiation of seismic wave on the fault plane, as well as the trend of the larger rupture area, the lower comer frequency, can be described by the source spectral model developed by the authors. A new dynamic comer frequency can be developed directly from the model. The dependence of ground motion on the size of subfault can be eliminated if this source spectral model is adopted in the synthesis. Finally, the approach presented is validated from the comparison between the synthesized and observed ground motions at six rock stations during the Northridge earthquake in 1994.展开更多
We developed a modified stochastic finite-fault method for estimating strong ground motions.An adjustment to the dynamic corner frequency was introduced,which accounted for the effect of the location of the subfault r...We developed a modified stochastic finite-fault method for estimating strong ground motions.An adjustment to the dynamic corner frequency was introduced,which accounted for the effect of the location of the subfault relative to the hypocenter and rupture propagation direction,to account for the influence of the rupture propagation direction on the subfault dynamic corner frequency.By comparing the peak ground acceleration(PGA),pseudo-absolute response spectra acceleration(PSA,damping ratio of 5%),and duration,the results of the modified and existing methods were compared,demonstrating that our proposed adjustment to the dynamic corner frequency can accurately reflect the rupture directivity effect.We applied our modified method to simulate near-field strong motions within 150 km of the 2008 MW7.9 Wenchuan earthquake rupture.Our modified method performed well over a broad period range,particularly at 0.04-4 s.The total deviations of the stochastic finite-fault method(EXSIM)and the modified EXSIM were 0.1676 and 0.1494,respectively.The modified method can effectively account for the influence of the rupture propagation direction and provide more realistic ground motion estimations for earthquake disaster mitigation.展开更多
In this study we performed a classical spectrum analysis of seismic waveforms recorded at far field stations of the great MW7.9 Wenchuan earthquake to observe the shifts of the corner frequency with azimuth due to the...In this study we performed a classical spectrum analysis of seismic waveforms recorded at far field stations of the great MW7.9 Wenchuan earthquake to observe the shifts of the corner frequency with azimuth due to the Doppler effect.Our results show that this damaging great earthquake had a dominating rupture propagation direction of 64.0°.The equivalent radius of the fault rupture surface was estimated to be 33 km,yielding the rupture area of about 3 500 km2.Thus the length of the rupture fault surface is about 230 km if the depth(or width) extent is 15 km.The computer program developed in this study can quickly provide the information about the source of a future large(damaging) earthquake,which could be very useful for predicting aftershocks and planning the rescue operations.展开更多
Broadband P and S waves source spectra of 12 M_s≥5.0 earthquakes of the 1997 Jiashi, Xinjiang, China. earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these ear...Broadband P and S waves source spectra of 12 M_s≥5.0 earthquakes of the 1997 Jiashi, Xinjiang, China. earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these earthquakes have been estimated through measuring the corner frequency of the source spectra. Direction of rupture propaga- tion of the earthquake faulting has also been inferred from the azimuthal variation of the comer frequency. The main results are as follows: ① The rupture size of M_s≥6.0 strong earthquakes is in the range of 10~20 km, while that of Ms_=5.0~5.5 earthquakes is 6~10 km. ② The static stress drop of the swarm earthquakes is rather low, being of the order of 0.1 MPa. This implies that the deformation release rate in the source region may be low. ③ Stress drop of the earthquakes appears to be proportional to their seismic moment, and also to be dependent on their focal mechanism. The stress drop of normal faulting earthquakes is usually lower than that of strike-slip type earth quakes. ④ For each M_s≥6.0 earthquake there exists an apparent azimuthal variation of the comer frequencies. Azimuthally variation pattern of comer frequencies of different earthquakes shows that the source rupture pattern of the Jiashi earthquake swarm is complex and no uniform rupture expanding direction exists.展开更多
The mainshock location of the Badong MsS. 1 earthquake is determined using four location methods : the simplex method, HYP2000, hyposat, and locSAT; the 350 aftershocks over 3 months are relocated using the double di...The mainshock location of the Badong MsS. 1 earthquake is determined using four location methods : the simplex method, HYP2000, hyposat, and locSAT; the 350 aftershocks over 3 months are relocated using the double difference location method. The results indicate that aftershocks are distributed as bands along the NEE direction and that the aftershocks 1 month after the mainshock, which are mainly distributed in the west of the mainshock and near the Gaoqiao fault, arc shallow earthquakes within 5 km; the depth of each after- shock after one month is deeper, and two distinct fault planes, for which the geological occurrence is similar to the Gaoqiao and Zhoujiashan-Niukou fault, are shaped. The frequency-spectrum analysis of the recorded wave- form in 12 seismic events indicates that the corner frequency of the mainshock is significantly lower than that of its aftershock and is also lower than a tectonic earthquake of the same magnitude. We considered that this result is related to the constraint of the parameter calibration relationship in the focal spectrum and the lithology change due to water erosion. Combined with the focal mechanism and geological tectonic setting, we conclude that the occurrence of the earthquake is related to the activity of the Daping and Gaoqiao fault and is a reser- voir-induced tectonic seismicity.展开更多
We computed source parameters for 143 earthquakes with M_L≥ 1. 0 occurring from January,2011 to March,2014 using waveform data recorded by the Nuozhadu and Jinghong Reservoir Seismic Networks. Then,the variation of s...We computed source parameters for 143 earthquakes with M_L≥ 1. 0 occurring from January,2011 to March,2014 using waveform data recorded by the Nuozhadu and Jinghong Reservoir Seismic Networks. Then,the variation of seismic activity and the characteristics of source parameters before and after the impoundment of the reservoir were investigated. The results show that:( 1) the seismic activity increased obviously after the impoundment,especially during the 3- 4 months after impoundment;( 2) the focal depths of the earthquakes occurring in the reservoir area are shallower than the earthquakes occurring outside the reservoir area in the initial stage of impoundment,but after a time,the difference was gradually reduced;( 3) corner frequency varies with the seismic moment and the log-linear relationship is more obvious after impounding;( 4)stress drop and apparent stress increase with increasing seismic moment,moreover they are lower for the earthquakes occurring in the reservoir area after impounding than those occurring outside the reservoir area or before impounding with the same seismic moment;( 5) the effect of reservoir impoundment on an earthquake can reach a depth of 10 km,and the maximum effect is seen at a depth of 3km- 6km,and the differences of seismic activity and average apparent stress between the inside and outside of the reservoir are significant.展开更多
The Ms7. 3 earthquake occurred in Yutian, Xinjiang on February 12, 2014. Based on seismic waveform data before the earthquake and aftershocks of the earthquake sequence, which were recorded by the Xinjiang Regional Di...The Ms7. 3 earthquake occurred in Yutian, Xinjiang on February 12, 2014. Based on seismic waveform data before the earthquake and aftershocks of the earthquake sequence, which were recorded by the Xinjiang Regional Digital Seismic Network, this paper corrected instrument response, propagation path and site response of the S-wave recording spectra. We then calculated with genetic algorithms, on the basis of the Brune model, the source parameters of the 102 M, ≥ 3. 0 Yutian earthquake sequence, seismic moment, apparent stress and corner frequency. The results show that, seismic moment of the earthquake sequence is between 3. 46 × 10^11 -2. 08×10^15N.m, apparent stress is between 1.48 × 10^5 -1.16 ×10^6Pa, mean stress level is 0. 31MPa, and corner frequency is between 1.4-7. 1Hz in the range of 3. 0 -5. 0. By analyzing the apparent stress and corner frequency variation with time, we obtain that apparent stress of earthquakes before the Yutian Ms7. 3 earthquake was significantly higher than the aftershock sequence, but the corner frequency was significantly lower than the aftershock sequence. Apparent stress was at a high level before the main shock, which shows that the main shock zone accumulated higher stress, and then the apparent stress was reduced. The main shock occurred in the process of slow increase. Because of the release of a large amount of stress, after the Ms7. 3 earthquake, the apparent stress was gradually reduced. That was the performance of low stress fracture of aftershocks.展开更多
基金National Natural Science Foundation of China Under Grant No. 50778058 and 90715038National Key Technology R&D Program Under Contract No. 2006BAC13B02
文摘In this paper, three existing source spectral models for stochastic finite-fault modeling of ground motion were reviewed. These three models were used to calculate the far-field received energy at a site from a vertical fault and the mean spectral ratio over 15 stations of the Northridge earthquake, and then compared. From the comparison, a necessary measure was observed to maintain the far-field received energy independent of subfault size and avoid overestimation of the long- period spectra/level. Two improvements were made to one of the three models (i.e., the model based on dynamic comer frequency) as follows: (i) a new method to compute the subfault comer frequency was proposed, where the subfault comer frequency is determined based on a basic value calculated from the total seismic moment of the entire fault and an increment depending on the seismic moment assigned to the subfault; and (ii) the difference of the radiation energy from each suhfault was considered into the scaling factor. The improved model was also compared with the unimproved model through the far-field received energy and the mean spectral ratio. The comparison proves that the improved model allows the received energy to be more independent of subfault size than the unimproved model, and decreases the overestimation degree of the long-period spectral amplitude.
基金supported by National Natural Science Foundation of China under grant No. 50778058 and 90715038National Key Technology Research and Development Program under grant No. 2006BAC13B02
文摘The static comer frequency and dynamic comer frequency in stochastic synthesis of ground motion from fi- nite-fault modeling are introduced, and conceptual disadvantages of the two are discussed in this paper. Furthermore, the non-uniform radiation of seismic wave on the fault plane, as well as the trend of the larger rupture area, the lower comer frequency, can be described by the source spectral model developed by the authors. A new dynamic comer frequency can be developed directly from the model. The dependence of ground motion on the size of subfault can be eliminated if this source spectral model is adopted in the synthesis. Finally, the approach presented is validated from the comparison between the synthesized and observed ground motions at six rock stations during the Northridge earthquake in 1994.
文摘We developed a modified stochastic finite-fault method for estimating strong ground motions.An adjustment to the dynamic corner frequency was introduced,which accounted for the effect of the location of the subfault relative to the hypocenter and rupture propagation direction,to account for the influence of the rupture propagation direction on the subfault dynamic corner frequency.By comparing the peak ground acceleration(PGA),pseudo-absolute response spectra acceleration(PSA,damping ratio of 5%),and duration,the results of the modified and existing methods were compared,demonstrating that our proposed adjustment to the dynamic corner frequency can accurately reflect the rupture directivity effect.We applied our modified method to simulate near-field strong motions within 150 km of the 2008 MW7.9 Wenchuan earthquake rupture.Our modified method performed well over a broad period range,particularly at 0.04-4 s.The total deviations of the stochastic finite-fault method(EXSIM)and the modified EXSIM were 0.1676 and 0.1494,respectively.The modified method can effectively account for the influence of the rupture propagation direction and provide more realistic ground motion estimations for earthquake disaster mitigation.
文摘In this study we performed a classical spectrum analysis of seismic waveforms recorded at far field stations of the great MW7.9 Wenchuan earthquake to observe the shifts of the corner frequency with azimuth due to the Doppler effect.Our results show that this damaging great earthquake had a dominating rupture propagation direction of 64.0°.The equivalent radius of the fault rupture surface was estimated to be 33 km,yielding the rupture area of about 3 500 km2.Thus the length of the rupture fault surface is about 230 km if the depth(or width) extent is 15 km.The computer program developed in this study can quickly provide the information about the source of a future large(damaging) earthquake,which could be very useful for predicting aftershocks and planning the rescue operations.
文摘Broadband P and S waves source spectra of 12 M_s≥5.0 earthquakes of the 1997 Jiashi, Xinjiang, China. earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these earthquakes have been estimated through measuring the corner frequency of the source spectra. Direction of rupture propaga- tion of the earthquake faulting has also been inferred from the azimuthal variation of the comer frequency. The main results are as follows: ① The rupture size of M_s≥6.0 strong earthquakes is in the range of 10~20 km, while that of Ms_=5.0~5.5 earthquakes is 6~10 km. ② The static stress drop of the swarm earthquakes is rather low, being of the order of 0.1 MPa. This implies that the deformation release rate in the source region may be low. ③ Stress drop of the earthquakes appears to be proportional to their seismic moment, and also to be dependent on their focal mechanism. The stress drop of normal faulting earthquakes is usually lower than that of strike-slip type earth quakes. ④ For each M_s≥6.0 earthquake there exists an apparent azimuthal variation of the comer frequencies. Azimuthally variation pattern of comer frequencies of different earthquakes shows that the source rupture pattern of the Jiashi earthquake swarm is complex and no uniform rupture expanding direction exists.
基金supported by the Spark Program of Earthquake Sciences(XH14035YSX)
文摘The mainshock location of the Badong MsS. 1 earthquake is determined using four location methods : the simplex method, HYP2000, hyposat, and locSAT; the 350 aftershocks over 3 months are relocated using the double difference location method. The results indicate that aftershocks are distributed as bands along the NEE direction and that the aftershocks 1 month after the mainshock, which are mainly distributed in the west of the mainshock and near the Gaoqiao fault, arc shallow earthquakes within 5 km; the depth of each after- shock after one month is deeper, and two distinct fault planes, for which the geological occurrence is similar to the Gaoqiao and Zhoujiashan-Niukou fault, are shaped. The frequency-spectrum analysis of the recorded wave- form in 12 seismic events indicates that the corner frequency of the mainshock is significantly lower than that of its aftershock and is also lower than a tectonic earthquake of the same magnitude. We considered that this result is related to the constraint of the parameter calibration relationship in the focal spectrum and the lithology change due to water erosion. Combined with the focal mechanism and geological tectonic setting, we conclude that the occurrence of the earthquake is related to the activity of the Daping and Gaoqiao fault and is a reser- voir-induced tectonic seismicity.
基金funded by the National Natural Science Foundation of China(Grant No.41174051)the National Science and Technology Pillar Program of the 12th"Five-year Plan"of China(Grant No.2012BAK19B02)
文摘We computed source parameters for 143 earthquakes with M_L≥ 1. 0 occurring from January,2011 to March,2014 using waveform data recorded by the Nuozhadu and Jinghong Reservoir Seismic Networks. Then,the variation of seismic activity and the characteristics of source parameters before and after the impoundment of the reservoir were investigated. The results show that:( 1) the seismic activity increased obviously after the impoundment,especially during the 3- 4 months after impoundment;( 2) the focal depths of the earthquakes occurring in the reservoir area are shallower than the earthquakes occurring outside the reservoir area in the initial stage of impoundment,but after a time,the difference was gradually reduced;( 3) corner frequency varies with the seismic moment and the log-linear relationship is more obvious after impounding;( 4)stress drop and apparent stress increase with increasing seismic moment,moreover they are lower for the earthquakes occurring in the reservoir area after impounding than those occurring outside the reservoir area or before impounding with the same seismic moment;( 5) the effect of reservoir impoundment on an earthquake can reach a depth of 10 km,and the maximum effect is seen at a depth of 3km- 6km,and the differences of seismic activity and average apparent stress between the inside and outside of the reservoir are significant.
基金jointly sponsored by the National Key Technology R&D Program of China(2012BAK19B04-01-05)the Youth Earthquake Situation Tracking Program of China Earthquake Administration(2015010106)
文摘The Ms7. 3 earthquake occurred in Yutian, Xinjiang on February 12, 2014. Based on seismic waveform data before the earthquake and aftershocks of the earthquake sequence, which were recorded by the Xinjiang Regional Digital Seismic Network, this paper corrected instrument response, propagation path and site response of the S-wave recording spectra. We then calculated with genetic algorithms, on the basis of the Brune model, the source parameters of the 102 M, ≥ 3. 0 Yutian earthquake sequence, seismic moment, apparent stress and corner frequency. The results show that, seismic moment of the earthquake sequence is between 3. 46 × 10^11 -2. 08×10^15N.m, apparent stress is between 1.48 × 10^5 -1.16 ×10^6Pa, mean stress level is 0. 31MPa, and corner frequency is between 1.4-7. 1Hz in the range of 3. 0 -5. 0. By analyzing the apparent stress and corner frequency variation with time, we obtain that apparent stress of earthquakes before the Yutian Ms7. 3 earthquake was significantly higher than the aftershock sequence, but the corner frequency was significantly lower than the aftershock sequence. Apparent stress was at a high level before the main shock, which shows that the main shock zone accumulated higher stress, and then the apparent stress was reduced. The main shock occurred in the process of slow increase. Because of the release of a large amount of stress, after the Ms7. 3 earthquake, the apparent stress was gradually reduced. That was the performance of low stress fracture of aftershocks.