Wen Xueze

(Sichuan Provincial Earthquake Bureau, Chengdu 610041)

Abstract The 900km-long main strike-slip active fault zone in western Sichuan exhibits a strong left-lateral Faulting is one of the main seismogenic zones in southwest China. This paper combines geological and historical seismic data to quantitatively assess the seismic potential of this fault zone. The average slip rate of the fault was recalculated or estimated, and the zone was divided into 16 segments based on the fault geometry and the spatio-temporal images of historical earthquake ruptures. Based on estimated coseismic slip, historical and prehistoric earthquake timing data, and using time-predictable and updateable models, the authors estimate the average earthquake recurrence time for each fault segment. The probability of future segment rupture earthquakes was further calculated using a time-dependent probabilistic hazard assessment model. The main results show: ① By 2026, 6 of the 16 fault sections will have a high cumulative earthquake probability (>0.45). These 6 sections are all located in empty sections along the fault zone that have not experienced rupture for at least 100 years. Medium; ② Since most of these six paragraphs have a longer average recurrence time or a shorter elapsed time than the average recurrence time, not all of them will have high earthquake conditions in the next 30 years (1996 to 2026). Probability; ③ Comparison of earthquake probabilities in different sections shows that: Qianning-Kangding (section 8-section 11) and Shimian-Xichang (section 14 and section 15) should belong to the relative risk areas of the fault zone in the future.

Keywords Seismically Potentially Active Faults in Western Sichuan

1 Introduction

The fault zone studied in this article runs through the entire western Sichuan region from northwest to southeast (Figure 1), with a total length of about 900km, composed of four faults, namely: Garze-Yushu fault, Xianshuihe fault, Anninghe fault and Zemuhe fault. Since the Late Quaternary, these faults all exhibit strong sinistral strike-slip faulting, and the average slip rate and its standard deviation have then been recalculated or estimated. The recalculated or estimated average slip rate is illustrated in Figure 3. In Figure 3, there are 9 locations where reliable geomorphological offset and sediment dating data can be obtained, so the calculated average sliding rate and its standard deviation can be obtained; the average sliding rate and its uncertainty of the other 3 locations in Figure 3 can be obtained Ranges (numbers in parentheses) are the result of reasonable speculation.

Figure 1: Index map of major strike-slip fault zones in western Sichuan showing the regional relationship between the studied fault zones and other major active faults in mainland China

Figure 3 shows: Garze-Yushu fault and Xian The Shuihe fault has a high sliding rate, reaching 10-14mm/a, but along the Anning River and Zemuhe faults, the sliding rate is only between 5.5-6.5mm/a. It can be seen from Figure 1 that there are many secondary branch faults around the Anning River and Zemu River faults. A possible reasonable explanation is that this secondary branch fault disperses the horizontal movement of the fault block, thereby reducing the slip rate along the main fault traces of the Anning River and Zemu River.

Figure 2. Technical roadmap for quantitative assessment of seismic risk in segments of active faults

3. Spatio-temporal images of historical earthquakes and their ruptures

For this fault He said that except for two parts, all the remaining parts contain historical earthquake data. Figure 4 is a set of plan views that plot the spatial distribution of historical earthquake sources in five periods from the early 18th century to the present. The scale of each earthquake source is circled based on the scope of the heavy damage zone during the earthquake.

In the past 250 years, the Luhuo-Daofu section of the fault zone has repeatedly experienced 2 to 3 historical earthquakes (Figure 4). This fault section also has the highest earthquake potential in the entire fault zone. Parts with sliding speed (13~14mm/a) (Figure 3). Therefore, the higher the slip rate along this fault zone, the higher the recurrence rate of earthquakes.

If the length of the earthquake source is taken as the corresponding rupture length, and these rupture lengths are used as a function of time, a spatio-temporal image of historical earthquake ruptures can be obtained (Figure 5). Figure 5 illustrates:

(1) In the part of the fault zone near Manigango, there is a space-time domain with no documented earthquake records, which means that for this fault part, except for one earthquake (approximately occurred around 1506 AD) was determined based on rough archaeological methods [3], and there is no documented earthquake data before the 18th century.