从库仑破裂应力和余震分布角度探讨汶川地震和芦山地震的关系

本文以龙门山及周边地区为研究对象,考虑区域地质构造差异、主要活动断裂带、地表附加重力影响,建立能反映地表起伏和岩石圈分层结构的龙门山地区三维粘弹性有限元模型。以地壳水平运动速率观测值为约束条件重建研究区现今构造背景应力场,在此基础上分别模拟了汶川地震和芦山地震的发生机理。通过分析同震库仑破裂应力变化与余震空间分布的关系,探讨了2次地震主震对余震的触发作用以及汶川地震对芦山地震的影响。研究表明,汶川地震和芦山地震的余震大部分由其主震触发,汶川地震对芦山地震的余震有约6.78%的触发作用。汶川地震的同震库仑破裂应力在芦山地震主震位置的增加值约为0.016MPa,如果龙门山断裂带南段库仑破裂应力年累积速率按照0.4×10-3-0.6×10-3MPa·a-1计算,汶川地震使芦山地震提前了约27-40年。计算还表明汶川地震和芦山地震的发生使鲜水河断裂带南段和虎牙断裂的库仑破裂应力增加,这些断裂带在未来发生地震的可能性增加。     

新疆天山地区的波速比异常分析

Based on the seismic observation report data provided by the Xinjiang Digital Seismic Network from 2009 to 2014,we calculate the wave velocity ratio and its background value for medium and small earthquakes by using the multi-station method in Tianshan,Xinjiang.This paper analyzes the variation of the wave velocity ratio disturbance value to highlight the abnormal,and also back-traces 7 moderate earthquakes at the research area.The results show that:(1)the background value of the wave velocity ratio is almost 1.70,the wave velocity ratio obviously decreases in the middle-eastern part of Tianshan and the region near the Puchang fault;(2)the wave velocity ratio disturbance value is mostly low in the epicenter before four earthquakes of M≥5.0 from 2011 to 2013 in the study area;(3)before 7 moderate strong earthquakes,the earthquake events with low value of the wave velocity ratio account for over 60% of corresponding total events near the epicenters,and the low value of the wave velocity ratio is relatively obvious before moderate earthquakes.     

龙门山断裂带上“破裂空段”的发震概率研究

本文采用分层粘弹性介质模型计算了汶川地震对芦山震中产生的库仑应力加载的影响,进而结合Dieterich(1994)提出的速率状态摩擦定律给出芦山附近区域6级地震累积发震概率随时间的变化。结果显示,2013年芦山7.0级地震时其累积发震概率达18%,说明汶川地震产生的应力扰动加速了芦山地震的发生。本文还计算了汶川、芦山2次地震对其间"破裂空段"处产生的累积库仑应力扰动的影响,结合背景地震发生率,给出了"破裂空段"处6级地震累积发震概率变化。虽然计算结果可能受到大邑地震、介质模型参数的选取和背景地震发生概率等因素影响而存在一定误差,但"破裂空段"在2次强震应力加载下累积发震概率是不断增大的,因此我们认为"破裂空段"处发生中强地震的紧迫性不断增强。     

Change of crustal gravitational potential energy in the Taiwan orogen by the Chi-Chi earthquake sequence

The active convergence between the northwest corner of the Philippine Sea Plate and the southeast margin of the Eurasian Plate has given rise to the Taiwan mountain-building and produced numerous earthquakes. Among the earthquakes, the 1999 Chi-Chi earthquake is the largest one recorded in the century. In this study, we examine the crustal gravitational potential energy (GPE) change in the Taiwan orogen caused by the Chi-Chi earthquake sequence, which was catalogued by the regional broadband seismometer array for a whole year. As a result, we find that the crust was going up and down randomly during the earthquake sequence, but an overall cumulative gain of the crustal GPE, +1.82×10¹⁶ J, was rapidly achieved in 1 month after the main shock. The crustal GPE was nearly still afterwards and reached +1.90×10¹⁶ J in 1 year. Spatially, although the main surface faulting has occurred in western Taiwan, the crustal GPE gain is mainly distributed in central Taiwan at the area where the existing crustal GPE is high and the existing lithospheric GPE is relatively low. The crustal GPE loss by the Chi-Chi earthquake sequence can also be observed and is generally distributed at both sides of the crustal GPE gain area. The crustal GPE gain mainly found in central Taiwan corroborates that the uplift of the Taiwan orogen is principally taking place in central Taiwan, rather than in the more hazardous western Taiwan.     

1624年“扬州地震”震中的新认识

公元1624年2月10日,即明代天启三年12月22日,在现今江苏省范围内发生了一次破坏性地震。在历次出版的地震目录中,扬州被确定为本次地震的震中,其主要依据为“扬州倒卸城垣三百八十余垛、城铺二十余处”的历史记述。《地震亘江南北疏》的发现为本次地震的研究提供了新的资料。本文分析已有资料的可靠性;选择相对可靠的历史资料划定Ⅵ度等烈度线;采用新划定的Ⅵ度等烈度线,按历史地震影响烈度的衰减关系确定本次地震的震级为6 1/4级;综合Ⅵ度等烈度线范围内的地震地质条件以及历史地震资料中人的感受、地表变形和各地地声方向记录,综合确定了震中位置大致在32.2°N、119.5°E,与1913年4月3日镇江5 1/2级地震(参考地名“江苏镇江”)震中相距不远。此外,本文还描述了本次地震的地震序列。     

2021年四川泸县M6.0地震发震机理及地震活动时空演化特征

2021年9月16日四川泸县发生M6.0地震, 该地震发震构造不明, 发震机理尚存在争议.地震精定位和震源机制有助于分析地震活动时空演化与震源破裂特征, 能够有效揭示活动构造机制和地震发生机理, 为评估区域地震危险性提供科学依据.为此, 本文首先采用双差定位法对震中及附近2009年1月至2021年10月发生的地震进行了精定位, 结果显示, 研究区地震震源深度大多集中在10 km范围内, 事件主要沿地表断层呈条带状或丛集分布, 部分震群邻近当地工业井, 周边无明显断层分布.其次, 通过CAP波形反演计算得到M≥3.5地震的震源机制解, 表明研究区震源破裂以逆冲挤压型为主, 部分震源机制解具有不确定性.基于震源机制解反演区域应力场, 进一步探讨了区域应力场与地震事件的力学一致性.研究结果显示, 区域应力场以水平构造挤压作用为主, 部分事件震源机制解与其吻合度较低, 暗示存在局部应力差异.综合地震活动时空演化特征、已知断层展布以及区域应力场等研究结果, 认为华蓥山断裂带南段的地震活动与资源开采活动密切相关, 泸县M6.0地震是在局部应力场扰动下, 下方滑脱层活动触发了上覆隐伏断层的挤压错动而产生.

     

新疆乌苏5.1级地震前波速比异常震例研究

利用天山中段数字化地震波资料,采用多台和达法,计算2006年11月23日新疆乌苏5.1级地震前后波速比的变化情况,得到如下结果:(1)在空间分布上,乌苏5.1级地震前,波速比形成一个近似椭圆形低值异常区,且椭圆长半轴约为70 km,短半轴约为55 km,椭圆走向NW,地震就发生在该椭圆区域的西北部边缘;(2)在时间进程...     

2014年云南景谷6.6级地震前后活动能量场分析

本文将地震释放能量作为地震活动场的基本要素, 采用自然正交函数展开方法, 系统研究2014年景谷6.6级地震震中区域地震活动能量场的时空特征。 结果表明, 景谷6.6级地震前能量场的前4个主要特征值对应的典型能量场时间因子都出现明显上升变或下降异常, 空间等值线形成局部能量高值异常危险区, 可能是景谷 6.6级地震空间异常的中短期特征。 我们还进一步研究了景谷6.6级地震前后空间异常随时间的演变, 给出了异常发展变化模式, 最后应用研究地震资料的累积次数从物理角度解释异常形成的机制。     

基于AHP的新疆南天山西段中强地震预测指标体系及效能评估

本文从新疆南天山西段地区映震效果较好的预测指标出发, 采用AHP(Analytic Hierarchy Process, 层次分析法)建立了新疆南天山西段地区预测指标体系。 在此基础上, 应用1～9比率标度法构建相应的判断矩阵, 进而计算各指标的权重。 结果显示, 几项映震效果较好的指标中, 权重值相对较大的是短期预测指标中的形变异常和部分测震学参数。 同时AHP模型也给出了新疆南天山西段有无中强地震的综合判断指标Y, Y值可较好地反映新疆南天山西段地区中强地震的震兆强弱程度和异常可靠性, 当Y≥2.191时, 新疆南天山西段地区短期内存在发生中强地震的危险。     

PAHs distribution in sediments associated with gas hydrate and oil seepage from the Gulf of Mexico

Six sediment samples collected from the Gulf of Mexico were analyzed. Total concentrations of the PAHs ranged from 52 to 403 ng g⁻¹ dry weight. The lowest PAH concentration without 5–6 rings PAHs appeared in S-1 sample associated with gas hydrate or gas venting. Moreover, S-1 sample had the lowest organic carbon content with 0.85% and highest reduced sulfur level with 1.21% relative to other samples. And, analysis of the sources of PAHs in S-1 sample indicated that both pyrogenic and petrogenic sources, converserly, while S-8, S-10 and S-11 sample suggested petrogenic origin. The distribution of dibenzothiophene, fluorine and dibenzofuran and the maturity parameters of triaromatic steranes suggested that organic matters in S-1 sample were different from that in S-8, S-10 and S-11 sample. This study suggested that organic geochemical data could help in distinguish the characteristic of sediment associated with gas hydrate or with oil seepage.