In this paper, we present a fast and fraction free procedure for computing the inertia of Bezout matrix and we can determine the numbers of different real roots and different pairs of conjugate complex roots of a pol...In this paper, we present a fast and fraction free procedure for computing the inertia of Bezout matrix and we can determine the numbers of different real roots and different pairs of conjugate complex roots of a polynomial equation with integer coefficients quickly based on this result.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
We assess the performance of waveform cross correlation as applied to automatic and interactive processing of the aftershock sequence of the April 11, 2012 Sumatera Ms（IDC） = 8.2 earthquake. The XSEL （cross correla...We assess the performance of waveform cross correlation as applied to automatic and interactive processing of the aftershock sequence of the April 11, 2012 Sumatera Ms（IDC） = 8.2 earthquake. The XSEL （cross correlation standard event list） is compared to the REB （Reviewed Event Bulletin） issued by the IDC （International Data Centre）. The latter includes 1,181 aftershocks between April 11 and May 25. To automatically recover the sequence, sixteen aftershocks were selected from the IDC SEL3 （Standard Event List） available on April 13 and used as master events. Waveform templates from only seven IMS （International Monitoring System） array stations with the largest SNR （signal-to-noise ratio） for the main shock were used to calculate cross correlation coefficients. Approximately 620,000 arrivals were detected and then used to build events according to the IDC definition. After conflict resolution between event hypotheses with similar arrivals found by more than one master, all survived hypotheses populated the XSEL. The total number of distinct hypotheses was 4,924, with 2,763 hypotheses not matched by the REB, i.e. potentially new REB events. To evaluate the quality of the XSEL, we randomly selected a representative portion （-15%） from 2,763 hypotheses and reviewed them interactively according to standard IDC rules and guidelines. There were 119 new REB events built and 145 XSEL hypotheses rejected. Several frequency and probability density distributions have been constructed for all detections, the associated detections, the XSEL detections, the detections in the new REB, and rejected events.展开更多
Using the joint inversion method with the amplitude ratio of P-wave,SV-wave and SHwaves,this paper calculates the focal mechanisms of the aftershock sequence of the Yaoan earthquake with MS6. 0. According to the spati...Using the joint inversion method with the amplitude ratio of P-wave,SV-wave and SHwaves,this paper calculates the focal mechanisms of the aftershock sequence of the Yaoan earthquake with MS6. 0. According to the spatial distribution of earthquake sequence,the author analyzes the characteristics of the stress field and seismogenic fault. The result shows that:( 1) the seismogenic fault of the Yaoan earthquake is a vertical right-lateral strike-slip fault,striking NWW-SEE. The result is reliable and consistent with the nodal planes of the Harvard CMT solution and also in accord with the predominant direction of aftershocks.( 2) The predominant direction of principal compressive stress,NWW-SEE is consistent with the regional tectonic stress,and some aftershocks are different from the main shock. The stress field of the main shock is controlled by the regional tectonic stress field,indicating the diversity and complexity in the seismic area.( 3) By comprehensively analyzing the distribution of the earthquake sequence,focal mechanism and fault structure in the seismic area,it is found that the Maweijing fault is the seismogenic fault of the Yaoan earthquake.展开更多
This paper briefly introduces the current research progress in the field of foreshocks,both in China and abroad,and contrasts the common characteristics and the mechanisms of foreshocks of the sequence under the defin...This paper briefly introduces the current research progress in the field of foreshocks,both in China and abroad,and contrasts the common characteristics and the mechanisms of foreshocks of the sequence under the definition of different conditions of foreshocks. The main recognition methods of foreshocks are briefly reviewed,and their characteristics and existing problems are reviewed and discussed. Foreshocks are small earthquakes that occur before the mainshock and adjacent to the main source location. A foreshock sequence is constituted of a series of foreshock activities that occur before the mainshock. The proportion of earthquake cases includes direct foreshocks ranging from 10% - 40% at different defined conditions of foreshocks. Theoretically,cascade model or pre-slid model can explain foreshocks. Foreshocks are mainly concentrated in the range of 10km -75 km of the mainshock,but their time distribution form is very complicated,mostly prior to the mainshock from 1 or 2 days,the seismicity rate of part of foreshock sequences shows significant acceleration features,but many foreshock sequences often show the attenuation characteristics of mainshock-aftershock sequences. The most prominent feature of foreshocks is a focal consistent mechanism and low b-value of earthquakes of the earthquake sequence. Foreshocks seems to have a certain relationship with tectonic environment and the rupture form of the mainshock,in limited foreshocks earthquake cases,the dip-thrusting earthquakes seem to have relatively more foreshocks. The results of some of the earthquake cases show that the focal depth of foreshocks gradually moved downward with the mainshock approaching. So far,it is difficult to determine whether an earthquake or an earthquake sequence is a foreshock or foreshock sequence before the mainshock. The identification methods of foreshocks mainly include a statistical method of analogy,focal consistent mechanism and related derivative method,the fine detection of the earthquake nucleation process. From a few existing studies of earthquake cases,in spite of earthquake temporal clusters and focal consistent mechanism being the most significant features of foreshock sequence,there were not sufficient conditions for judging a foreshock sequence. Because the rupture rate of expansion and sliding displacement have a tendency to increase faster with time,the method of fine detection of the earthquake nucleation process is expected to play a more important role in the identification of foreshocks,but it needs more earthquake examples to be verified.展开更多
文摘In this paper, we present a fast and fraction free procedure for computing the inertia of Bezout matrix and we can determine the numbers of different real roots and different pairs of conjugate complex roots of a polynomial equation with integer coefficients quickly based on this result.
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.
文摘We assess the performance of waveform cross correlation as applied to automatic and interactive processing of the aftershock sequence of the April 11, 2012 Sumatera Ms（IDC） = 8.2 earthquake. The XSEL （cross correlation standard event list） is compared to the REB （Reviewed Event Bulletin） issued by the IDC （International Data Centre）. The latter includes 1,181 aftershocks between April 11 and May 25. To automatically recover the sequence, sixteen aftershocks were selected from the IDC SEL3 （Standard Event List） available on April 13 and used as master events. Waveform templates from only seven IMS （International Monitoring System） array stations with the largest SNR （signal-to-noise ratio） for the main shock were used to calculate cross correlation coefficients. Approximately 620,000 arrivals were detected and then used to build events according to the IDC definition. After conflict resolution between event hypotheses with similar arrivals found by more than one master, all survived hypotheses populated the XSEL. The total number of distinct hypotheses was 4,924, with 2,763 hypotheses not matched by the REB, i.e. potentially new REB events. To evaluate the quality of the XSEL, we randomly selected a representative portion （-15%） from 2,763 hypotheses and reviewed them interactively according to standard IDC rules and guidelines. There were 119 new REB events built and 145 XSEL hypotheses rejected. Several frequency and probability density distributions have been constructed for all detections, the associated detections, the XSEL detections, the detections in the new REB, and rejected events.
文摘Using the joint inversion method with the amplitude ratio of P-wave,SV-wave and SHwaves,this paper calculates the focal mechanisms of the aftershock sequence of the Yaoan earthquake with MS6. 0. According to the spatial distribution of earthquake sequence,the author analyzes the characteristics of the stress field and seismogenic fault. The result shows that:( 1) the seismogenic fault of the Yaoan earthquake is a vertical right-lateral strike-slip fault,striking NWW-SEE. The result is reliable and consistent with the nodal planes of the Harvard CMT solution and also in accord with the predominant direction of aftershocks.( 2) The predominant direction of principal compressive stress,NWW-SEE is consistent with the regional tectonic stress,and some aftershocks are different from the main shock. The stress field of the main shock is controlled by the regional tectonic stress field,indicating the diversity and complexity in the seismic area.( 3) By comprehensively analyzing the distribution of the earthquake sequence,focal mechanism and fault structure in the seismic area,it is found that the Maweijing fault is the seismogenic fault of the Yaoan earthquake.
基金supported by the Special Task for Science and Technology Project of the Department of Earthquake Monitoring and Prediction,CEA in 2016(1640501320212)
文摘This paper briefly introduces the current research progress in the field of foreshocks,both in China and abroad,and contrasts the common characteristics and the mechanisms of foreshocks of the sequence under the definition of different conditions of foreshocks. The main recognition methods of foreshocks are briefly reviewed,and their characteristics and existing problems are reviewed and discussed. Foreshocks are small earthquakes that occur before the mainshock and adjacent to the main source location. A foreshock sequence is constituted of a series of foreshock activities that occur before the mainshock. The proportion of earthquake cases includes direct foreshocks ranging from 10% - 40% at different defined conditions of foreshocks. Theoretically,cascade model or pre-slid model can explain foreshocks. Foreshocks are mainly concentrated in the range of 10km -75 km of the mainshock,but their time distribution form is very complicated,mostly prior to the mainshock from 1 or 2 days,the seismicity rate of part of foreshock sequences shows significant acceleration features,but many foreshock sequences often show the attenuation characteristics of mainshock-aftershock sequences. The most prominent feature of foreshocks is a focal consistent mechanism and low b-value of earthquakes of the earthquake sequence. Foreshocks seems to have a certain relationship with tectonic environment and the rupture form of the mainshock,in limited foreshocks earthquake cases,the dip-thrusting earthquakes seem to have relatively more foreshocks. The results of some of the earthquake cases show that the focal depth of foreshocks gradually moved downward with the mainshock approaching. So far,it is difficult to determine whether an earthquake or an earthquake sequence is a foreshock or foreshock sequence before the mainshock. The identification methods of foreshocks mainly include a statistical method of analogy,focal consistent mechanism and related derivative method,the fine detection of the earthquake nucleation process. From a few existing studies of earthquake cases,in spite of earthquake temporal clusters and focal consistent mechanism being the most significant features of foreshock sequence,there were not sufficient conditions for judging a foreshock sequence. Because the rupture rate of expansion and sliding displacement have a tendency to increase faster with time,the method of fine detection of the earthquake nucleation process is expected to play a more important role in the identification of foreshocks,but it needs more earthquake examples to be verified.
