Neotectonics of the Kharaulakh sector of the Laptev Shelf

Seismotectonic deformation and crustal stress pattern have been studied comprehensively in major seismogenic structures of the Kharaulakh sector of the Verkhoyansk fold system and adjacent parts of the Chersky seismotectonic zone. The study focuses on neotectonic structures, deep structure, and systems of active faults, as well as tectonic stress fields inferred by tectonophysical analysis of Late Cenozoic faults and folds. The results, along with geological and geophysical data, reveal main strain directions and structural patterns of crustal stress and strain in the Arctic segment of the Eurasia-North America plate boundary. The area is a junction of mid-ocean and continental structures evolving in a mixed setting of extension, compression, and their various combinations. The rotation pole of the two plates is presumably located near Buor-Khaya Bay. In this case, extension is expected to act currently upon the neotectonic structures north of the bay and compression to control those in the south and southeast. This inference is consistent with the identified zoning of stress and strain in the Kharaulakh sector.     

Focal mechanisms of recent earthquakes in the Southern Korean Peninsula

We evaluate the stress field in and around the southern Korean Peninsula with focal mechanism solutions, using the data collected from 71 earthquakes ( M_L = 1.9–5.2) between 1999 and 2004. For this, the hypocentres were relocated and well-constrained fault plane solutions were obtained from the data set of 1270 clear P -wave polarities and 46 SH / P amplitude ratios. The focal mechanism solutions indicate that the prevailing faulting types in South Korea are strike-slip-dominant-oblique-slip faultings with minor reverse-slip component. The maximum principal stresses (σ₁) estimated from fault-slip inversion analysis of the focal mechanism solutions show a similar orientation with E–W trend (269°–275°) and low-angle plunge (10°–25°) for all tectonic provinces in South Korea, consistent with the E–W trending maximum horizontal stress (σ_Hmax) of the Amurian microplate reported from in situ stress measurements and earthquake focal mechanisms. The directions of the intermediate (σ₂) and minimum (σ₃) principal stresses of the Gyeongsang Basin are, however, about 90 deg off from those of the other tectonic provinces on a common σ₂–σ₃ plane, suggesting a permutation of σ₂ and σ₃. Our results incorporated with those from the kinematic studies of the Quaternary faults imply that NNW- to NE-striking faults (dextral strike-slip or oblique-slip with a reverse-slip component) are highly likely to generate earthquakes in South Korea.     

云南孟连西7.3级、武定6.5级、丽江7.0级三次强震前地震波振幅比的时空演化特征

１９９５年７月１２日至１９９６年２月３日短短７个月,云南地区连续发生了孟连西中缅边境７．３级、武定５．５级、丽江７．０级３次强震,本文研究了近期这几次强震前５个地震台地震图垂直分量Ｓ、Ｐ波最大振幅比的时空演化特征,动态追踪了振幅比明显偏离平稳态的突变过程。发现主震前５—８年,７级大震震中１００ｋｍ范围出现振幅比高（低）值突变,６级强震震中１３０ｋｍ范围出现振幅比高值突变,当振幅比的突变在缓升（降）的背景上骤升（降）,或突变异常的地震次数明显增加,则中长期异常进入中短期阶段。在强震震中１３０ｋｍ范围内的地震台（近台）振幅比值高达１５．２以上,而远离强震震中２５０ｋｍ以外的地震台（远台）振幅比最大值仅为９．８,近台的突变幅度至少比远台大３０％。而强震成组发生前一年半时间内,位于强震震中１１０ｋｍ范围内的近台振幅比的突变幅度比远在２５０ｋｍ外远台大５５—７５％。对振幅比的突变和时空演化特征从非线性动力学模型和模拟实验结果进行了初步成因探讨。     

南北地震带等地区强地震在华北中南部的“响应地震”研究

2008年5月12日T14:28汶川发生8.0级大地震,2008年5月13日T5:00江苏省发生滨海ML3.8地震。滨海地震是否是由汶川地震触发的、可指示滨海附近中短期内将发生中强地震的"诱发前震"?基于此,本文进行了如下研究:①统计南北地震带及中国台湾7.3级以上、日本7.5级以上大地震;②统计①中大震发生后3天时间(72 h)内,华北中南部地区发生的M_L 3以上地震;③统计大震发生后1年内在M_L 3地震附近地区(距震中350 km以内)发生的5级以上地震;④对上述3组地震是否存在链式关系进行统计研究,即研究特定条件下的A—F—B链式地震现象在华北中南部的预报效果。研究结果表明:根据目前所拥有的统计资料,无法确定2008年5月13日滨海M_L 3.8地震是由汶川8级地震诱发的"前兆地震"。     

Earthquakes,catastrophic sediment additions and the response of urban stream communities

Disturbance events can regularly impact stream ecosystems; however, large-scale catastrophic disturbances are rare. From September 2010 to September 2011 Christchurch City experienced over 8500 earthquakes including a magnitude 7.1. One consequence was catastrophic additions of silt and sand into waterways throughout the city. Of 161 km of permanent waterways, 102 km (63%) were affected by earthquake siltation. Benthic invertebrates and fish communities were compared across 16 streams with differing siltation. Invertebrate taxonomic richness decreased significantly (mean 17 taxa reduced to 10 taxa) and EPT taxa (Ephemeroptera, Plecoptera and Trichoptera) were removed entirely from streams receiving heavy siltation. Fish richness and density decreased significantly, with fish absent from some heavily silted streams. Many of these urban streams are sourced from springs and their stable flows and low gradient limit their ability to flush sediment. We predict that without human intervention there will be a long-term sediment legacy and it may take many years for these streams to recover from this catastrophic disturbance.     

地震预报思路的再讨论

文中回顾了1974年提出的“块、带、源、兆、触、报”六字预报思路，并基于近20年来的研究对此进行了补充和深化。     

Potential Seismic Risk in Taiwan Strait Region

GPS observation indicates that the Fujian coastal region of China mainland, the region of Taiwan Strait and northern Taiwan island all show a generally homogenous horizontal motion with weak deformation. Historical earthquake record over more than 800 years and modern instrumental data reveal that there is potential seismic risk in and around Taiwan Strait region. After the National Seismic Zoning Map of China (2001) the expected seismic risk in northern part of the Taiwan Strait is lower than that in middle and southern part. The suggested northern route of the Taiwan Strait passage project seems to be relatively save seismically.     

Countermeasures for breakwater foundation subjected to foreshocks and main shock of earthquake loading

Coastal protective structures, such as composite breakwaters, are generally vulnerable to earthquake. It was observed that breakwaters damage mainly due to failure of their foundations. However, the seismically induced failure process of breakwater foundation has not been well understood. This study describes failure mechanism of breakwater foundation as well as a newly developed reinforcing model for breakwater foundation that can render resiliency to breakwater against earthquake-related disasters. Steel sheet piles and gabions were used as reinforcing materials for foundation. The experimental program consisted of a series of shaking table tests for conventional and reinforced foundation of breakwater. Numerical analyses were conducted using finite difference method, and it was observed that the numerical models were capable to elucidate the seismic behavior of soil–reinforcement–breakwater system. This paper presents an overview of the results of experimental and numerical studies of the seismic response of breakwater foundation. Overall, the results of these studies show the effectiveness of the reinforced foundation in mitigating the earthquake-induced damage to the breakwater. Moreover, numerical simulation was used for parametric study to determine the effect of different embedment depths of sheet piles on the performance of breakwater foundation subjected to seismic loading.     

南海周边相对海平面变化特征及2004年苏门答腊地震影响分析

利用南海周边1989-2014年的潮汐资料和GPS长期观测资料,分析了南海周边相对海平面变化特征,以及2004年苏门答腊地震对该区域相对海平面变化的影响。研究结果表明,南海周边的相对海平面变化以上升为主,平均上升速率（4.53±0.20） mm/a,高于全球平均速率,且2004年后上升趋势加剧;南海周边相对海平面呈现6类较典型的变化特征,并存在与板块构造相对应的分区聚集现象,形成了中国东南和越南沿海、马来半岛、加里曼丹岛北部、菲律宾群岛等4个变化特征区。受2004年苏门答腊大地震的影响,马来半岛、南沙和西沙海域的地壳形变由上升趋势转为下沉,加剧了相对海平面的上升;中国东南沿海和菲律宾群岛受地震影响较小;越南沿海和加里曼丹岛北部区域的地震影响还有待进一步研究。     

漫湾水库蓄水前后库区地震活动性与构造应力场分析

对漫湾水库蓄水诱发地震作了分析，结果表明，蓄水后库区小震频次明显增加，近距离地震明显增多，在蓄水首次达到高水位和由高水位突降至低水位时，诱发了最强地震。表明蓄水对库区构造应力场产生了影响，使得局部应力场较区域构造应力场作用方向出现明显偏转，作用方式发生改变，呈现较大的垂直作用效应，节面错动出现较大正倾滑动分量。