The April 2007 earthquake swarm near Lake Trichonis and implications for active tectonics in western Greece

We investigate the properties of the April 2007 earthquake swarm (Mw 5.2) which occurred at the vicinity of Lake Trichonis (western Greece). First we relocated the earthquakes, using P- and S-wave arrivals to the stations of the Hellenic Unified Seismic Network (HUSN), and then we applied moment tensor inversion to regional broad-band waveforms to obtain the focal mechanisms of the strongest events of the 2007 swarm. The relocated epicentres, cluster along the eastern banks of the lake, and follow a distinct NNW–ESE trend. The previous strong sequence close to Lake Trichonis occurred in June–December 1975. We applied teleseismic body waveform inversion, to obtain the focal mechanism solution of the strongest earthquake of this sequence, i.e. the 31 December 1975 (Mw 6.0) event. Our results indicate that: a) the 31 December 1975 Mw 6.0 event was produced by a NW–SE normal fault, dipping to the NE, with considerable sinistral strike-slip component; we relocated its epicentre: i) using phase data reported to ISC and its coordinates are 38.486°N, 21.661°E; ii) using the available macroseismic data, and the coordinates of the macroseismic epicentre are 38.49°N, 21.63°E, close to the strongly affected village of Kato Makrinou; b) the earthquakes of the 2007 swarm indicate a NNW–SSE strike for the activated main structure, parallel to the eastern banks of Lake Trichonis, dipping to the NE and characterized by mainly normal faulting, occasionally combined with sinistral strike-slip component. The 2007 earthquake swarm did not rupture the well documented E–W striking Trichonis normal fault that bounds the southern flank of the lake, but on the contrary it is due to rupture of a NW–SE normal fault that strikes at a  45° angle to the Trichonis fault. The left-lateral component of faulting is mapped for the first time to the north of the Gulf of Patras which was previously regarded as the boundary for strike-slip motions in western Greece. This result signifies the importance of further investigations to unravel in detail the tectonics of this region.     

Spatio-temporal evolution of Coulomb stress in the Pacific slab inverted from the seismicity rate change and its tectonic interpretation in Hokkaido, Northern Japan

We estimated spatio-temporal evolution of Coulomb stress within the subducted Pacific slab in Hokkaido from the analysis of seismicity rate change. For this purpose we used earthquake catalog from the Institute of Seismology and Volcanology (ISV), Hokkaido University for the period 1993/4/1–2006/12/31 after relocating to compensate location errors due to the heterogeneous P- and S-wave structure beneath Hokkaido. We found that spatial pattern of Coulomb stress change inverted from the seismicity rate change is comparable with static change in Coulomb stress estimated from dislocation models. Our results and analyses reveal important insights on spatio-temporal pattern of deformation of the subducted Pacific slab in terms of Coulomb stress change. We found that the 2003 Tokachi Oki earthquake (Mw = 8.0) pervasively perturbed Coulomb stress in a regional scale with a significant impact to trigger the 2004 Kushiro Oki earthquake. The 2004 Kushiro Oki earthquake (Mw = 7.0) is another significant stressing event that changed the pattern of Coulomb stress in the area. We found that stressing events with magnitude smaller than 7.0 has minimal impact on Coulomb stress change in the Pacific slab. Similarly, comparatively deep focused large earthquakes could not change Coulomb stress significantly. Further the pattern of Coulomb stress change after the 2003 Tokachi Oki earthquake correlates the pattern of afterslip distribution in Hokkaido.     

地震预测试验场的回顾与展望

地震预测试验场针对特定的地震危险区，通过密集的、多学科的强化观测，研究与短临地震预测有关的科学问题，作为一类“大科学”项目，地震预测试验场的经验和教训值得认真总结，本文回顾和评述了地震预测试验场的观测与研究，对地震预测试验场的概念进行了分析和讨论，指出新技术的应用赋予地震预测试验场以新的内涵。并为地震预测研究带来新的发展机遇。     

预测发震时间的水氡滑动变化率值及其检验

介绍了水氡滑动变化率的计算公式，滑动变化率的演化与地震时间的统计关系，据此给出了水氡滑动变化率值发震时间预测的步骤、判断指标和方法。结合震例，对预测效能进行了评价。检验性预测结果表明，预测的发震期限为1－12个月，平均5．1个月。该方法可以用于强震中短期预报。     

首都圈断层形变空间信息合成图像

用四点组斜率信息法全时空处理了首都圈全部跨断层短水准和短基线测量资料，然后以观测台9或测点）为单位，将同一处多条测线的资料进行了信息合成，得到了以台点经纬度为坐标，以合成结果为信息量的形变前兆信息的空间分布序列图像。这些图像随时间的变化类似气象云图，对首都圈附近6级以上强震分布撤离位有一定的批示意义。     

地震监测中的电阻率层析技术

将电阻率层析技术应用于地震监测,由视电阻率值重建出介质的真电阻率图像,取得了较好效果.在宝坻台和昌黎台设立的两个试验点上于1998年4月14日ML5.0和ML4.4唐山两次地震前的6天左右层析图像出现了明显的异常变化:宝坻台的电阻率图像一改通常的在平稳背景上叠加小量随机变化的特点,出现了一种有序性特征的新图样;昌黎台也出现了反差加大、高低阻区集中分布的有序性特征.上述异常图样均在震后消失.层析图像在震前出现的熵值降低可能是这次地震活动的前兆.地层导电结构和孔隙度的变化,是引起电阻率异常的直接原因.研究表明,常规的单一极距的视电阻率测量之所以对真电阻率的变化不敏感且丧失空间分辨能力,是由于该物理量同时具有积分值和位函数这两个固有特征所决定的.在地震监测中,改造现行观测系统,引入层析成像,是发展技术的方向.     

岩石圈塑性流动波的实验研究(Ⅰ)

实验采用了适当配比的塑化松香 ,模拟岩石圈延性层 ,研究边界驱动条件下塑性流动波的传播过程。实验表明 ,塑性流动波类似于粘性重力波 ,并有“快波”和“慢波”之分 ,二者分别由主波和辅波叠加而成。主波类似于孤立波或涌波。根据相似原理 ,“快波”主波的外推波速约为 0 .12～2 .5km/a ,在波速量级上大致相当或接近于岩石圈下层某些控制地震迁移的塑性流动波     

云南大理地区温泉CO2释放与地震预报研究

通过对大理地区鹤庆、洱源、下关、弥渡等温泉水CO2释放特征及与区域地震活动的相关性研究，提炼出单项地震预报指标，从而进行系统合成，找出大理地区CO2的综合预报指标。     

青藏高原东缘礼县-罗家堡断裂带晚更新世以来的活动性分析

礼县 -罗家堡断裂带晚更新世以来有过明显活动。在礼县—罗家堡段和天水镇—街子口段直接错断全新世地层。断裂沿线地表陡坎发育 ,水系被左旋位错。结合沿该断裂带广泛分布的地震滑坡、砂土液化等 ,认为礼县 -罗家堡断裂带是 1654年天水南 8级地震的发震构造。该断裂晚更新世以来的平均水平位错速率为 0 95mm/a ,平均垂直位移速率为 0 35mm/a ,垂直位移速率约为水平位移速率的 1/ 3。这个比值与一次断裂突发性垂直位错量 ( 1 9m)与水平位错量 ( 5 2m)的比值基本吻合     

强震概率增大时段判定法TIP-M8在广东省及邻区的应用

用强震概率增大时段判定法M8方法判断近年来广东省及邻区几个主要震区(粤闽赣地区、粤桂琼地区、珠江三角洲地区)的中期地震发展趋势,结果显示1997年5月福建永安5.2级地震,1999年5月海南5.1级地震,震前约1年半,地震所在区域均出现了强震概率增大时段.而珠江三角洲地区的计算结果未发现强震概率增大时段.