Region-time-length algorithm and its application to the study of intermediate-short term earthquake precursor in North China

Abstract

The Region-Time-Length Algorithm (RTL algorithm) is introduced and improved in the paper. Compared with the original definition, the influence of rupture length on RTL function is emphasized and the weights of epicentral distance function, time function, and rupture length function are ensured to be equal. The retrospective examinations of RTL algorithm in North China have indicated that the anomalies obtained by the improved RTL algorithm show the short or intermediate-short term precursory features in most cases. There are two types of RTL anomalous patterns before the main shock. For the I-type, the variation pattern of theVRTL, numerical values of theVRTL(x, y, z, t) function, is complete and most of them have shown the changing pattern of “rising from 0 “ turning “ dropping” or ”dropping from 0 ” turning ” rising”. For the II-type, the variation pattern ofV RTL is not complete, which increases or decreases quickly from 0 and there is no evident turning, the main shock generally occurs in the short period around the peakVRTL. The rising ofVRTL indicates an increase of seismic activity relative to the background level, which means the enhancement of seismic activity, while the dropping ofV RTL indicates the decrease of seismic activity relative to the background level, which represents the seismic quiescence to a certain extent. According to statistical examination results of RTL algorithm in North China, the methods to distinguish the intermediate and short-term anomalies and to estimate the occurrence time of the coming main shock are given in the paper. For both I and II-type RTL anomalies, the R-value,i.e., the forecasting score, is about 0.6 and 0.3 for the 3 months forecasting period and about 0.7 and 0.4 for the 6 months forecasting period. The preliminary discussion is also made for the influences of characteristic time-spant0, characteristic distancer0, and threshold magnitudeM 0 on computation ofV RTL, as well as some other significant problems in application.