REGIONAL CHARACTERISTICS OF STRESS STATE OF MAIN SEISMIC ACTIVE FAULTS IN MID‐NORTHERN PART OF SICHUAN‐YUNNAN BLOCK

IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS 地球物理学报 Pub Date : 2017-05-01 DOI:10.1002/CJG2.30043
Wu Weiwei, Wu Peng, W. Yaling, Sun Wei
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引用次数: 8

Abstract

We restore the seismic source spectrums of 1012 earthquakes (2.0 ≤ ML ≤ 5.0) in the mid-northern part of Sichuan-Yunnan seismic block between January 1, 2009 and December 31, 2015, then calculate the source parameters (e.g., seismic moments M0, focal scale r and stress drop Δσ) and fit the calibration relationship between these parameters. Based on the regional seismic tectonic background, the distribution of active faults and seismicity, the study area is divided into four statistical units. For each unit the stress distribution characteristics, change of stress drop with location, correlation between the stress-strain loading and the dynamic process of regional deformation, are discussed respectively. The results show that seismic moments M0 are consistent with the magnitude-moment relation that lgM0 = 0.92ML + 10.46. The relationship between stress drop and magnitude is consistent with the result gained by Nuttli that intraplate earthquake follows the ISD model, with a statistical relationship lgΔσ = 0.31 lgM0 – 3.92. Seismic source stress drop results show the following, (1) The stress at the end of the Jinshajiang fault is low, the overall sliding rate of the fault unit is high, and strong earthquake activity is very rare. In the fault belt consisting of three secondary faults, stress-strain loading deceases gradually from northwest to southeast along Litang fault, the northwest section which is relatively locked is more likely to accumulate strain than southeast section. (2) Stress drop of Xianshuihe fault zone is divided by Kangding, the southern section is low and northern section is high. Southern section (Kangding-Shimian) is difficult to accumulate higher strain in the short term, but in northern section (Garze-Kangding), moderate and strong earthquakes have not filled the gaps of seismic moment release, there is still a high stress accumulation in partial section. (3) High stress-drop events were concentrated on Anninghe-Zemuhe fault zone, strain accumulation of this unit is strong, and stress level is the highest, earthquake risk is high. (4) On Lijiang-Xiaojinhe fault zone, stress drop characteristics of different magnitude earthquakes are not the same, which is related to complex tectonic setting, the specific reasons still need to be discussed deeply. Stress background in the Muli area is low and may be affected by the local tectonic environment. The study also shows that, (1) Stress drops display a systematic change with different faults and locations, high stress-drop events occur mostly in the fault intersection area. Faults without locking condition and mainly creeping are mainly characterized by low stress drop. (2) Contrasting to what is commonly thought that “strike-slip faults are not easy to accumulate stress”, Xianshuihe fault zone and Anninghe-Zemuhe fault zone all exhibit high stress levels, which may be due to that the magnitude and intensity of medium-strong earthquakes are not enough to release the accumulated energy. On the other hand, in the complex dynamics of regional deformation, when the tectonic force blocking fault movement and its contribution to accumulation of stress plays a key role, the earthquake of same magnitude will release higher stress drop.
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川滇地块中北部主要地震活动断裂应力状态的区域特征
对2009年1月1日至2015年12月31日川滇震区中北部1012次地震(2.0≤ML≤5.0)的震源谱进行恢复,计算震源参数(地震矩M0、震级r和应力降Δσ),并拟合这些参数之间的标定关系。根据区域地震构造背景、活动断层分布和地震活动性,将研究区划分为4个统计单元。分别讨论了各单元的应力分布特征、应力降随位置的变化、应力-应变加载与区域变形动态过程的关系。结果表明,地震矩M0符合lgM0 = 0.92ML + 10.46的震级矩关系。应力降与震级的关系与Nuttli的板内地震遵循ISD模型的结果一致,统计关系lgΔσ = 0.31 lgM0 - 3.92。震源应力降结果表明:(1)金沙江断裂末端应力低,断裂单元整体滑动速率高,强震活动极少。在由三条次级断裂组成的断裂带中,沿理塘断裂,应力-应变载荷由西北向东南逐渐减小,相对封闭的西北段比东南段更容易积累应变。(2)鲜水河断裂带应力降以康定为界,南段低,北段高。南段(康定—石面)短期内难以积累较高应变,而北段(甘孜—康定)中、强地震尚未填补地震矩释放的空白,部分地段仍存在较高的应力积累。(3)高应力降事件集中在安宁河-则木河断裂带,该单元应变积累强,应力水平最高,地震危险性高。(4)在丽江—小金河断裂带,不同震级地震的应力降特征不尽相同,这与复杂的构造环境有关,具体原因仍需深入探讨。木里地区应力背景较低,可能受局部构造环境的影响。研究还表明:(1)应力降随断层和断层位置的不同呈现出系统的变化,高应力降事件多发生在断层交汇区;无锁断条件、以爬行为主的断层,其主要特征是应力降小。(2)与“走滑断层不易积聚应力”不同,鲜水河断裂带和安宁河-则木河断裂带均表现出较高的应力水平,这可能是由于中强震的震级和烈度不足以释放积聚的能量所致。另一方面,在复杂的区域变形动力学中,当构造力对断层运动的阻断作用及其对应力积累的贡献发挥关键作用时,相同震级的地震将释放更高的应力降。
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来源期刊
地球物理学报
地球物理学报 地学-地球化学与地球物理
CiteScore
3.40
自引率
28.60%
发文量
9449
审稿时长
7.5 months
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