Research on Strong Earthquake Tendency on Active Tectonic Block Boundaries in the Chinese Mainland

Previous studies have shown that the active tectonic block boundaries in the Chinese mainland are the main belts and concentration areas of strong earthquakes occurring in the Chinese mainland.It is essential to carry out follow-up analysis of strong earthquake risk of active tectonic block boundaries.In this paper,we carry out the analysis on the tendency of strong earthquakes along each active tectonic block boundary from three aspects respectively,including the evolutionary characteristics of the Load/Unload Response Ratio time series,the probability method based on the log-normal distribution function,and variation of b value.The estimation of strong earthquake criticality on each active tectonic block boundary is done based on the evolutionary characteristics of the Load/Unload Response Ratio time series,the cumulative probability and conditional probability,and the decrease of the b value.Finally,according to the results of analyses on the above three aspects,the potential strong earthquake areas in the forthcoming 5 years in the Chinese mainland are discussed.

Retrospection on the Conclusions of Earthquake Tendency Forecast before the Wenchuan M_S8.0 Earthquake

The reason for the failure to forecast the Wenchuan Ms 8.0 earthquake is under study, based on the systematically collection of the seismicity anomalies and their analysis results from annual earthquake tendency forecasts between the 2001 Western Kunlun Mountains Pass Ms8. 1 earthquake and the 2008 Wenchuan Ms8.0 earthquake. The results show that the earthquake tendency estimation of Chinese Mainland is for strong earthquakes to occur in the active stage, and that there is still potential for the occurrence of a Ms8.0 large earthquake in Chinese Mainland after the 2001 Western Kuulun Mountains Pass earthquake. However the phenomena that many large earthquakes occurred around Chinese Mainland, and the 6-year long quietude of Ms7.0 earthquake and an obvious quietude of Ms5.0 and Ms6.0 earthquakes during 2002- 2007 led to the distinctly lower forecast estimation of earthquake tendency in Chinese Mainland after 2006. The middle part in the north-south seismic belt has been designated a seismic risk area of strong earthquake in recent years, but, the estimation of the risk degree in Southwestern China is insufficient after the Ning＇er Ms6.4 earthquake in Yunnan in 2007. There are no records of earthquakes with Ms ≥ 7.0 in the Longmenshan fault, which is one of reasons that this fault was not considered a seismic risk area of strong earthquakes in recent years.

The Rhythm of Earthquake Activity and an Analysis on the Earthquake Tendency of the World, the Chinese Continent and North China

Based on the Morlet complex wavelet transformation,the authors put forward a kind of new method for distinguishing periods of seismic activity and quietude and a new physical thought on the time-dependent wavelet accumulation energy spectrum with periods, the time-frequency distribution of wavelet vibration period spectrum and period-specific wavelet vibration spectrum. By applying the above methods to a time series which is composed of earthquake accumulation energy per year for the world, the Chinese continent and North China, respectively, we obtained some new information about the rhythm of shallow earthquake activity. Considering the historic earthquakes and the rhythm characteristics of current strong earthquake activity, the earthquake tendency in the next years is discussed.

Tracing the Forecast of Earthquakes Based on the Seismicity Characteristics of the Chi-Chi Strong Earthquake Swarm Sequence

The data of earthquakes with M ≥3 0 during the 7 years from September 21, 1993 to September 20, 2000 recorded by the Taiwan Central Weather Bureau (CWB) show that there were 6 types of clear characteristics of seismicity during the Chi Chi strong earthquake swarm of September 21 These 6 types of characteristics are (1) foreshock types, (2) seismic gaps, (3) seismic bands, (4) clustering activity of foreshocks and signal shock, (5) quiescence before the main shock and (6) secondary aftershocks in the aftershock sequence. Using the procedures for analyzing the yearly strong earthquake tendency, further tracing based on the earthquake sequence characteristics, and taking the Chi Chi earthquake sequence as an example, tracing analysis of the earthquake tendency was attempted using the shorter time range of monthly rather than in a yearly time scale. An attempt was made to establish the procedures for tracing analysis of shallow focus earthquakes in the seismic belt of western Taiwan. It is hoped that this can provide an analystical method for approaching the short imminent time scale of seismometry based earthquake forecasting.