Stochastic Characteristic-slip Model And Its Application Method

Since Reid (1910) developed the well-known elastic rebound theory of earthquake occurrence, until recently it has been the basis for most efforts at predicting the probability of strong earthquake recurrence (Shimazaki and Nakata,1980; Savage and Cockerham,1987). In the1980’s, the concept of " Characteristic earthquake " was derived from the study of actual records of seismicity and the study of geology (Schwartz and Coppersmith,1984; Aki,1984). Characteristic earthquake is proof that the fault segments along active faults can rupture independently(Ding,1992), which offer an actual proof of using probability model of strong earthquake recurrence in the Probabilistic Seismic Hazard Analysis (PSHA).A Stochastic Characteristic-slip model (SCS) is presented to calculate the occurring probability of large earthquakes, assuming different fault segments all fit the Characteristic Earthquake Model and the average seismic moment accumulation rate of each rupture source is a constant. In the SCS model, the magnitude and the recurrence interval of Characteristic earthquake are directly correlated.Two different methods of determining the parameters for different seismic-geological conditions are given in this paper, Simultaneously, the parameters uncertainties are researched and expressed quantitatively.The aim of proposing the Stochastic Characteristic-slip model (SCS) is to calculate the occurring probability of large earthquakes so that to provide the foundation for PSHA, rather than just for long-term earthquake prediction. On the basis of the Stochastic Characteristic-slip model (SCS), the application method of SCS in PSHA is researched. This study developed a method of probabilistic seismic hazard analysis, which consider top level rupture sources in the study area separately, the time distribution and the magnitude distribution obey the SCS, while the space distribution obey the Characteristic model in which large earthquakes recur in situ. Then consider the uncertainty of fault geometrical parameters, the result of probability seismic hazard analysis depending time can be obtained.Using the SCS model to calculate the conditional probability that an earthquake occurs in the next few decades, the time that it has not occurred in the last T years is needed. However, the elapsed time since the last earthquake is not available on some fault segments. Moreover, the Poisson model may underestimate the possibility of the occurrence of major earthquakes. For the active faults where the historical strong earthquake records are absent, a new method for calculating the conditional probability has been proposed by using the length of time with confirmed record of quiet as a parameter(Ts).For some major faults, the magnitude of Characteristic earthquakes on secondary rupture sources can still be very large. To calculate the probabilities of large earthquakes on secondary ruptures by the SCS model, distributing the cumulative rate of seismic moment to different levels of ruptures is necessary.There are two situations:One is that in the absence of paleoseismic or historical records of earthquakes on the secondary rupture sources, there are only the relative occurrence rates which are given by geologists. In view of this situation, a distribution method of the cumulative rate of seismic moment is presented, which is based on the principle of seismic moment-balance, the second is in the region where paleoseismic or historical records of earthquake data is available, the maximum possible cumulative rates of seismic moment on the secondary rupture sources can be obtain by paleoseismic and historical earthquake data. To illustrate this method, the Haiyuan fault is studied as an example.Considering the variability of the cumulative rates of seismic moment on fault segments, A improved Stochastic Characteristic-slip model is presented, in which fault interaction and stress triggering were considered simultaneously. This essay takes the northwestern portion of the Xianshuihe fault zone as the research area, and use the Monte Carlo method randomly generate mid-small earthquake sequences and the threshold values of the characteristic earthquake magnitude in the accumulation process of the seismic moment, and then simulate the major earthquake sequences in the northwestern portion of the Xianshuihe fault zone over the next50years which include both single-segment rupture and cascade rupture. Through analyzing millions of synthesized earthquake sequences, the probability of earthquake occurrence of great earthquake can be achieved.