Abstract: Based on the result of quantitative research on active faults,analysis of regional seismicity,and especially the detailed investigation and systematic summary on paleoearthquake in Urumqi region,the recurrence mode and probability models of Xishan Faults that reflect the seismic,geological and kinemics characteristics are established.The strong earthquake recurrence mode considers the Poisson mode and quasi-period mode and reflects the randomicity and determination with chanciness of seismicity on the fault.The probability model involves two levels of content:analyzing the paleoearthquake data and historical strong earthquake catalog on or near the faults to obtain the mean recurrence interval of surface-rupturing earthquakes(M_S≥6.7),and analyzing the modern instrumental earthquake catalog(1970～present,and the size of these earthquakes is in the range of 2.0～5.0) of potential seismic source zone where the active faults locate.The calculation of seismic hazard probability of active faults utilizes the expert-opinion method to assign different weights to the models such as Poisson model and BPT model,and then incorporate the weighted probability result to construct combined model,which is the core of the method.This data-processing method has two advantages:taking complexity of strong earthquake recurrence mode into consideration and reducing the possibility of overestimating the seismic hazard of active faults.The result shows that the recurrence probability of surface rupturing earthquakes is 4.0% in the coming 100 years,and 3.6% in the coming 50 years.This result is consistent with that of the method based on stress environment analysis.The maximum magnitude of Xishan Faults(belt)is M_S 7.5 estimated from paleoearthquake,dimension and dip-slip rate of fault,which is consistent with the upper limit magnitude of potential seismic source zone where the faults locate.This study integrates the newest research results on regional seismology and geology,better describes the complexity of seismic process along fault to a certain extent,and assesses comprehensively seismic hazards of active faults in Urumqi.This multidisciplinary method can be applied to the region like Urumqi where complete seismogeological data are unavailable.

Key words: active faults, seismic hazard, probability model, potential seismic zone

摘要： 基于乌鲁木齐地区活动断裂的定量研究和区域地震活动性的分析,特别是对活动断裂(带)上的古地震和现代地震资料进行的系统、详细的分析与总结,以西山断裂为例,建立了反映该断裂地震地质特点和运动学属性的复发模式和概率模型。复发模式的建立兼顾了泊松和准周期2种模式。概率模型的建立包括2个层次上的内容:分析断裂上的古地震和历史强震目录(1863—2006年)以获得地表破裂型地震(M_S≥6.7)的平均复发间隔;分析活动断裂所在潜在震源区的现代地震目录(1970—2006年,M_S=2.0～5.0)以确定中等以上地震(M_S≥5.0)的平均复发间隔;利用专家意见法组合相应的Poisson模型和BPT模型计算活动断裂各级地震的复发概率。计算结果表明,西山断裂地表破裂型地震的100a发震概率为4.0%,50a发震概率为3.6%。另外根据古地震资料、断裂规模和倾向滑动速率获得的西山断裂(带)的最大发震能力为7.5级。该研究综合应用了本地区的最新地震地质研究成果,在一定程度上较好地描述了断裂上地震活动的复杂性,可以较全面地评估乌鲁木齐地区活动断裂的地震危险性,该研究方法适合于地震地质资料较难完整获取的地区。

关键词: 活动断裂, 地震危险性, 概率模型, 潜在震源区