Outburst floods caused by breaches of landslide dams may cause serious damages and loss of lives in downstream areas; for this reason the study of the dynamic of the process is of particular interest for hazard and ri...Outburst floods caused by breaches of landslide dams may cause serious damages and loss of lives in downstream areas; for this reason the study of the dynamic of the process is of particular interest for hazard and risk assessment. In this paper we report a field-scale landslide dam failure experiment conducted in Nantou County, in the central of Taiwan.The seismic signal generated during the dam failure was monitored using a broadband seismometer and the signal was used to study the dam failure process.We used the short-time Fourier transform(STFT) to obtain the time–frequency characteristics of the signal and analyzed the correlation between the power spectrum density(PSD) of the signal and the water level. The results indicate that the seismic signal generated during the process consisted of three components: a low-frequency band(0–1.5 Hz), an intermediate-frequency band(1.5–10 Hz) and a highfrequency band(10–45 Hz). We obtained the characteristics of each frequency band and the variations of the signal in various stages of the landslide dam failure process. We determined the cause for the signal changes in each frequency band and its relationship with the dam failure process. The PSD sediment flux estimation model was used to interpret the causes of variations in the signal energy before the dam failure and the clockwise hysteresis during the failure. Our results show that the seismic signal reflects the physical characteristics of the landslide dam failure process. The method and equipment used in this study may be used to monitor landslide dams and providing early warnings for dam failures.展开更多
Based on the extraction and calculation of the short-term seismic precursory information magnitude from the 114 major precursory observations in the North China region, and together with consideration of factors such ...Based on the extraction and calculation of the short-term seismic precursory information magnitude from the 114 major precursory observations in the North China region, and together with consideration of factors such as geological structure, seismicity, crustal thickness, and in particular, the current geodynamics of the region, the authors studied the time-space evolution characteristics of the short-term earthquake precursory information magnitude and its relationship with earthquakes and proposed the index and method for the short-term synthetic prediction of earthquakes with M S≥5.0 in the North China region. The inspection through R-value shows that the method is effective to a certain extent for earthquake prediction.展开更多
There are controversies on ground motion attenuation relations at the epicentral distance of about 100km. Some models predict that the seismic energy remains almost constant or becomes even stronger with increasing di...There are controversies on ground motion attenuation relations at the epicentral distance of about 100km. Some models predict that the seismic energy remains almost constant or becomes even stronger with increasing distance at this distance, while other models hold that it decreases with increased distance. The divergence lies mainly in whether SmS is stronger than direct S and surface waves at this distance. With the MsS. 9 earthquake sequence in the Yingjiang region of Yunnan Province as an example, we demonstrate that SmS is always 2 - 5 times stronger than direct S waves around the epicentral distance of 100km （which is the post-critical distance for S in this region）. Study of synthetic seismograms suggest that crustal structure has an important effect on the amplitude of post-critical SmS, with simple crust producing strong SmS. This preliminary study confirms that in China, SmS also plays an important role on ground motion at distances around 100km, which demands more studies of post-critical SmS.展开更多
Although seismic gap theory plays an important role in the med-and long-term earthquake prediction,the potential risk of the non-seismic gap in historical earthquake rupture areas will need to be simultaneously taken ...Although seismic gap theory plays an important role in the med-and long-term earthquake prediction,the potential risk of the non-seismic gap in historical earthquake rupture areas will need to be simultaneously taken into account in the study of med-and long-term earthquake prediction,due to the temporally clustering or non-linear behavior of large earthquake recurrence.In order to explore technical methods which can be based on observational data,and identify historical earthquake rupture zones( including the seismic gap in historical and prehistoric earthquake rupture zones),we select eight historical large earthquake rupture zones with different elapsed times on the mid-north segment of the North-South Seismic Belt to make quantitative analysis on the characteristics of modern seismicity of these zones and preliminarily explore the seismicity method for determining the urgency degree of potential earthquake hazards.The results mainly show that the pvalue,which reflects the attenuation of earthquake sequence,and the a-value,which reflects the seismicity rate,are strongly related to the elapsed time of the latest earthquake in the rupture zone.However,the corresponding relationships in some rupture areas are not clear perhaps due to the complex fault structure and faulting behavior.The b-value,which represents the state of tectonic stress accumulation,does not easily reflect the elapsed time information of different evolution stages.The b-value temporal scanning shows a steady evolution over time in most of the rupture zones,but in the rupture zone of the Wudu M8.0 earthquake of 1879,the b-value shows significant fluctuations with a decreasing trend for 20 years.By comparative analysis,we conclude that the rupture zones of the 1933 M7.5 Maoxian earthquake and the 1976 M7.2 Songpan-Pingwu earthquake are still in the decaying period of earthquake sequences,and thus do not have the background for recurrence of M7.0 earthquakes.The low b-value Maqu segment,which is located at the north margin of the rupture zone of the 842A.D.M7.0 Diebu earthquake,is more dangerous than the Diebu segment.The continuous decline of the b-value in the 1879 M8.0 Wudu earthquake rupture zone may also indicate a new round of seismogenic process.展开更多
基金financially supported by the External Cooperation Program of Bureau of International Co-operation,Chinese Academy of Sciences(131551KYSB20130003)the Risk Evaluation and Mitigation Technology of Barrier Lake Project of China Communications Construction Company Limited(2013318J01100)+2 种基金the Key Technologies R&D Program of Sichuan Province in China(2014SZ0163)the Special Program for International S&T Cooperation projects of China(Grant No.2012DFA20980)National Natural Science Foundation of China(Grant No.51479179)
文摘Outburst floods caused by breaches of landslide dams may cause serious damages and loss of lives in downstream areas; for this reason the study of the dynamic of the process is of particular interest for hazard and risk assessment. In this paper we report a field-scale landslide dam failure experiment conducted in Nantou County, in the central of Taiwan.The seismic signal generated during the dam failure was monitored using a broadband seismometer and the signal was used to study the dam failure process.We used the short-time Fourier transform(STFT) to obtain the time–frequency characteristics of the signal and analyzed the correlation between the power spectrum density(PSD) of the signal and the water level. The results indicate that the seismic signal generated during the process consisted of three components: a low-frequency band(0–1.5 Hz), an intermediate-frequency band(1.5–10 Hz) and a highfrequency band(10–45 Hz). We obtained the characteristics of each frequency band and the variations of the signal in various stages of the landslide dam failure process. We determined the cause for the signal changes in each frequency band and its relationship with the dam failure process. The PSD sediment flux estimation model was used to interpret the causes of variations in the signal energy before the dam failure and the clockwise hysteresis during the failure. Our results show that the seismic signal reflects the physical characteristics of the landslide dam failure process. The method and equipment used in this study may be used to monitor landslide dams and providing early warnings for dam failures.
文摘Based on the extraction and calculation of the short-term seismic precursory information magnitude from the 114 major precursory observations in the North China region, and together with consideration of factors such as geological structure, seismicity, crustal thickness, and in particular, the current geodynamics of the region, the authors studied the time-space evolution characteristics of the short-term earthquake precursory information magnitude and its relationship with earthquakes and proposed the index and method for the short-term synthetic prediction of earthquakes with M S≥5.0 in the North China region. The inspection through R-value shows that the method is effective to a certain extent for earthquake prediction.
基金sponsored by the Basic Scientific Research Specific Program (02092410),Institute of Earthquake Science,China Earthquake Administration
文摘There are controversies on ground motion attenuation relations at the epicentral distance of about 100km. Some models predict that the seismic energy remains almost constant or becomes even stronger with increasing distance at this distance, while other models hold that it decreases with increased distance. The divergence lies mainly in whether SmS is stronger than direct S and surface waves at this distance. With the MsS. 9 earthquake sequence in the Yingjiang region of Yunnan Province as an example, we demonstrate that SmS is always 2 - 5 times stronger than direct S waves around the epicentral distance of 100km （which is the post-critical distance for S in this region）. Study of synthetic seismograms suggest that crustal structure has an important effect on the amplitude of post-critical SmS, with simple crust producing strong SmS. This preliminary study confirms that in China, SmS also plays an important role on ground motion at distances around 100km, which demands more studies of post-critical SmS.
基金funded jointly by National Science&Technology Pillar Program,China(Grant No.2012BAK19B01)the Task-oriented Contract for Seismic Regime Monitoring(2010020304)
文摘Although seismic gap theory plays an important role in the med-and long-term earthquake prediction,the potential risk of the non-seismic gap in historical earthquake rupture areas will need to be simultaneously taken into account in the study of med-and long-term earthquake prediction,due to the temporally clustering or non-linear behavior of large earthquake recurrence.In order to explore technical methods which can be based on observational data,and identify historical earthquake rupture zones( including the seismic gap in historical and prehistoric earthquake rupture zones),we select eight historical large earthquake rupture zones with different elapsed times on the mid-north segment of the North-South Seismic Belt to make quantitative analysis on the characteristics of modern seismicity of these zones and preliminarily explore the seismicity method for determining the urgency degree of potential earthquake hazards.The results mainly show that the pvalue,which reflects the attenuation of earthquake sequence,and the a-value,which reflects the seismicity rate,are strongly related to the elapsed time of the latest earthquake in the rupture zone.However,the corresponding relationships in some rupture areas are not clear perhaps due to the complex fault structure and faulting behavior.The b-value,which represents the state of tectonic stress accumulation,does not easily reflect the elapsed time information of different evolution stages.The b-value temporal scanning shows a steady evolution over time in most of the rupture zones,but in the rupture zone of the Wudu M8.0 earthquake of 1879,the b-value shows significant fluctuations with a decreasing trend for 20 years.By comparative analysis,we conclude that the rupture zones of the 1933 M7.5 Maoxian earthquake and the 1976 M7.2 Songpan-Pingwu earthquake are still in the decaying period of earthquake sequences,and thus do not have the background for recurrence of M7.0 earthquakes.The low b-value Maqu segment,which is located at the north margin of the rupture zone of the 842A.D.M7.0 Diebu earthquake,is more dangerous than the Diebu segment.The continuous decline of the b-value in the 1879 M8.0 Wudu earthquake rupture zone may also indicate a new round of seismogenic process.
