On the migration of precursors of strong earthquakes

It is found that perturbations presumedly associated with swarms, the B patterns and the BG pattern precursors of strong earthquakes in New Zealand, California and Apennines, propagate in the crust of the Earth with a velocity of the order of cm¹. The hypothesis that a single travelling elastic perturbation causes a set of precursors of the same strong earthquake is discussed and it is concluded that each precursor is associated with a different perturbation.     

Energy and tectonics of Fennoscandian earthquakes

Energy-time release curves are calculated for Swedish and for Fennoscandian earthquakes, both curves exhibiting a sharp break around the year 1910. The similarity of this behaviour with world-wide energy release curves suggests that Fennoscandian earthquakes are related to the global tectonics, probably via plate motions on the border between the North Atlantic and the Eurasian continent.     

On generation conditions of strong earthquakes in southern Baikal

In this paper the features of seismic process in the southern depression of Lake Baikal are considered. By the data on focal mechanisms of the earthquakes of February 25, 1999 (M _w = 6.0), and August 27, 2008 (M _w = 6.3), as well as based on configuration of their aftershock fields, it is determined that foci of strong seismic events in southern Baikal are controlled by the greatest structural elements of sublatitudinal and submeridional strikes. It has been shown that a substantial role in the formation of focal zones is played by low-scale destruction of the Earth’s crust, revealed by geological-geophysical data and proved by clustering of seismic shocks. New data on the August 27, 2008, earthquake have proved the high level of seismic danger of this part of the Baikal Rift Zone and allowed us to determine generation conditions of strong earthquakes more precisely.     

电磁辐射对台湾强震的反应

本文通过对 1 999年 9月 2 1日台湾南投 7 6级强震前电磁辐射变化特征的分析 ,进一步探讨了电磁辐射在短临预报中的作用 ,同时给出了初步判断震中位置的方法     

用小波方法检验强震“前驱波”

基于前人整理的前驱波特征和小波变换理论,应用小波方法分析了2001年11月14日昆仑山口西MS8.1和2004年12月26日苏门答腊MS8.7地震前30天山东泰安台体应变观测分钟值的高通滤波数据。研究表明,在昆仑山口西MS8.1地震前,高通滤波数据和小波分析结果比较正常。苏门答腊MS8.7地震前,高通滤波数据呈与气压相关变化,无明显异常,但小波分析结果细节部分第1、2层在12月5日左右有类似前驱波信号出现,波幅变化在±0.5×10-9之间,主要周期成分在2～4分钟之间,持续时间1天左右,与同时段气压变化形态不一致,对这种异常现象需要做进一步的分析。小波变换能够提取出体应变资料中的微弱变化信号,是检验强震前驱波的一种有效方法。     

Quiescence period prior to strong earthquakes in the Kuril-Kamchatka zone

The characteristics of the distributions of the time differences occurrence of the consecutive earthquakes in the Kuril-Kamchatka zone, including the Hokkaido Island area, have been investigated in various magnitude ranges. For the purpose of the analysis, we used the data from the regional and world earthquake catalogs for the last 20 years. As a result of this analysis, a new intermediate-term precursor effect has been found: a quiescence period observed prior to the strongest earthquakes. This precursor manifests itself in the form of the long-term (2–6 months) absence of events with M ≥ 5.5 within the territory. For the predictive purposes, it was proposed to replace the quiescence period by such a more stable parameter as the sum of the three longest intervals between the earthquakes with M ≥ 5.0 in a sliding time window. The prognostic informativeness of this parameter has been assessed.     

Investigation of the variability of strong ground motions from Vrancea earthquakes

A systematic investigation of the applicability of several ground motion prediction models for Vrancea intermediate-depth seismic source is conducted in this research. Two ground motion prediction models recommended by previous evaluations (Vacareanu et al. in Bull Earthq Eng 11(6):1867–1884, 2013a; Pavel et al. in Earthq Struct 6(1):1–18, 2014), as well as two new state-of-the-art ground motion prediction equations (Vacareanu et al. in J Earthq Eng, 2013b; Earthq Struct 6(2):141–161, 2014) are tested using an increased strong ground motion database consisting of 150 recordings from Vrancea subcrustal earthquakes. The evaluation is performed by using several goodness-of-fit parameters from the literature. Moreover, the applicability of the single-station sigma method is also investigated by using the same strong ground motion database recorded in 30 seismic stations from southern and eastern Romania. The influence of the soil conditions on the numerical results obtained in this study is investigated and discussed using the results provided by the analysis of variance method. The impact of the single-station standard deviation on the levels of seismic hazard is also assessed in this study, and the results show, in the analyzed cases, significant reductions of the hazard levels.     

Damage characteristics and influence factors of mountain tunnels under strong earthquakes

A total of 81 mountain tunnels that were damaged in 10 strong earthquakes are studied. They are classified into six typical damage characteristics: lining cracks, shear failure of lining, tunnel collapse caused by slope failure, portal cracking, leaking, and deformation of sidewall/invert damage. Further study and discussion are carried out on influencing factors for mountain tunnels, including seismic parameters, structural information, and rock conditions. Suggestions are also made regarding seismic resistance and reduction.     

Multiarchive paleoseismic record of late Pleistocene and Holocene strong earthquakes in Switzerland

A multiarchive approach has been applied to the investigation of the late Pleistocene and Holocene record of strong earthquakes in Switzerland. The geological archives used for this study include active faults, lake deposits, slope instabilities, and caves. In the Basle area, eight trenches were opened across the Basle–Reinach fault, nearby rockfall deposits were systematically investigated, sediment cores were taken from two lakes, and nine caves were studied. In Central Switzerland, five lakes were investigated by means of high-resolution seismic lines and sediment cores. Furthermore, three caves were studied in Central Switzerland. Altogether, the investigations are based on more than 350 km of high-resolution reflection seismic lines, 450 m of core samples, 260 m of trenches, and 245 radiocarbon age determinations. The measured co-seismic displacements along the Basle–Reinach fault supply independent information for the magnitude of the AD 1356 Basle earthquake exclusively based on geological evidence. Deformation features related to three well-documented strong historic earthquake shocks were identified. Deformation features of the AD 1774 Altdorf and AD 1601 Unterwalden earthquakes can be used to calibrate paleoseismic evidence in Central Switzerland. Altogether, traces of 13 earthquakes could be found in the two study areas, all of them with magnitudes M_w  6 or greater. For the first time, the earthquake catalogue for Switzerland can be extended back beyond historic records, into the late Pleistocene, spanning 15,000 years.     

Recurrence of strong earthquakes in the active Hovd Fault Zone, Mongolian Altay

A geological, geomorphic, and paleoseismological study of paleoseismodislocation systems has been carried out. Numerous indications of prehistoric strong earthquakes expressed in sediments deposited in the fault-line region due to the formation of transient barrier lakes were revealed in the active Hovd Fault Zone on the eastern slope of the Mongolian Altay during a paleoseismological study of young near-surface sediments in trenches and dug pits. The paleosoils buried by these sediments were radiocarbon-dated. It has been established that the strongest earthquakes with magnitudes of ～8, which took place here 7200, 6600, 1500, and later than 700 years ago, substantially changed the topography in the epicentral zone. By analogy with the results of paleoseismological investigations performed in the Gorny Altay and the western Mongolian Altay, the data obtained shed light on the recurrence of the strongest seismic events in the Great Altay.     

Characteristics of global strong earthquakes and their implications for the present-day stress pattern

Earthquakes occurred on the surface of the Earth contain comprehensive and abundant geodynamic connotations, and can serve as important sources for describing the present-day stress field and regime. An important advantage of the earthquake focal mechanism solution is the ability to obtain the stress pattern information at depth in the lithosphere. During the past several decades, an increasing number of focal mechanisms were available for estimating the present-day stress field and regime. In the present study, altogether 553 focal mechanism data ranging from the year 1976 to 2017 with Mw \(\ge \)7.0 were compiled in the Global/Harvard centroid moment tensor (CMT) catalogue, the characteristics of global strong earthquakes and the present-day stress pattern were analyzed based on these data. The majority of global strong earthquakes are located around the plate boundaries, shallow-focus, and thrust faulting (TF) regime. We grouped 518 of them into 12 regions (Boxes) based on their geographical proximity and tectonic setting. For each box, the present-day stress field and regime were obtained by formal stress inversion. The results indicated that the maximum horizontal principal stress direction was \(\sim \)N–S-trending in western North America continent and southwestern Indonesia, \(\sim \)NNE–SSW-trending in western Middle America and central Asia, \(\sim \)NE–SW in southeastern South America continent and northeastern Australia, \(\sim \)NEE–SWW-trending in western South America continent and southeastern Asia, \(\sim \)E–W-trending in southeastern Australia, and \(\sim \)NW–SE-trending in eastern Asia. The results can provide additional constraints to the driving forces and geodynamic models, allowing them to explain the current plate interactions and crustal tectonic complexities better.     

Horizontal motions and the generation of strong earthquakes in the North Sakhalin interiors

The recent geodynamics of Sakhalin Island is best described by the convergence of the Eurasian and North American (Sea of Okhotsk) lithospheric plates, which is manifested in the high seismic activity of the island. In North Sakhalin, the plate boundary is thought to correspond to a system of roughly N-S-trending faults, which belong to the North Sakhalin deep fault, and the Upper-Piltun fault; the latter was ruptured by the 1995 M 7.2 Neftegorsk earthquake. This study first confirmed that the stationary motion of the Sea of Okhotsk plate is retarded on this fault to form with time a series of drag folds and stress field anomalies. The latter are released during the subsequent (in a 400⦒o 1000-year period) strong earthquakes by seismic sliding on the flanks of the Upper Piltun fault. The 2003–2006 GPS observations revealed the free state of this fault zone with relative slip rates of 5–6 mm/yr.     

Thermal infrared anomalies as a precursor of strong earthquakes in the distant future

Satellite thermal infrared images contain valuable earthquake precursor information. Past studies concluded that such information appeared only a few days or dozens of days before an earthquake would occur. In our study, though, we observed that the time intervals between the thermal infrared precursor and an earthquake??s occurrence can be up to 10?years. An infrared image can also synchronously indicate the locations of additional future earthquakes with different epicenters within a region. The shape, area, intensity, and movement of thermal infrared anomaly areas are a combination of all the future strong earthquakes within a region. These distant future earthquakes are generally located near the edges, endpoints, or corners of the main structure, fine structures or periphery structures of a thermal infrared anomaly area and play a role in confining the anomaly area. There have not been any exceptions among the strong earthquakes we analyzed, which have included the 2011 Japan M _w 9 event, the 2010 Yushu M _S 7.1 event, the 2008 Wenchuan M _S 8 event, and many other strong events following the 2004 Sumatra M _S 9 event. Surprisingly, some of the earthquakes can outline an area of elevated temperature observed many months ago. If we can roughly locate these potential epicenters through the analysis of thermal infrared images and combining the analysis with other information, and then dynamically monitor them, it may be easier to observe the precursor of an earthquake and predict its occurrence.     

Identification of potential areas for the occurrence of strong earthquakes in Himalayan arc region

Morphostructural zoning (MSZ) scheme of the Himalayan arc region as obtained from a joint study of topographic, geological and tectonic maps as well as satellite imagery is analysed. Three types of morphostructures have been determined: territorial units (blocks of different ranks), linear zones limiting these blocks (lineaments) and intersections of the lineaments (knots). Comparison of MSZ scheme with the know seismicity indicates epicenters of strong earthquakes (M≥6·5) clustered around some of these knots. Pattern recognition method is used to determine seismically potential areas for the occurrence of recognition method is used to determine seismically potential, for the occurrence of strong earthquakes of magnitude ≥M ₀. We have carried out two such studies for the Himalayan arc region, one forM ₀=6·5 and the other forM ₀=7·0. Out of a total number of 97 knots, 48 knots are found to be seismically potential for the occurrence of earthquake ofM≥6·5. The results of the study forM ₀=6·5 were presented in the symposium on “Earthquake Prediction” held in Strasbourg, France, March 1991 (Gorshkovet al 1991). The epicenter of Uttarkashi earthquake of magnitude,M _b=6·6 that occurred in the late hours of 19th October 1991 (UTC) lies in the vicinity of one such knot. The second study carried out subsequently shows that only 36, knots are potential for the occurrence of earthquakes ofM≥7·0, which include the knot, associated with theUttarkashi earthquake.