Damage assessment of the 2015 Mw 8.3 Illapel earthquake in the North-Central Chile

Natural Hazards - Destructive megathrust earthquakes, such as the 2015 Mw 8.3 Illapel event, frequently affect Chile. In this study, we assess the damage of the 2015 Illapel Earthquake in the...     

Response of the Laprak,Nepal, landslide to the 2015 Mw 7.8 Gorkha earthquake

Natural Hazards - Coseismic displacements estimated from comparison before-and-after satellite images suggest that the large and intermittently active landslide upon which the village of Laprak,...     

Observation of abnormal thermal and infrasound signals prior to the earthquakes: a study on Bonin Island earthquake M7.8 (May 30, 2015)

Scientists from all over the world try to incorporate multi-disciplinary precursors to forecast the earthquake on a short-term basis. The authors here have analyzed outgoing longwave radiations acquired from polar-orbiting National Oceanic and Atmospheric Adminstration (NOAA) satellites and long-period infrasound waves recorded by the ground observatories in China prior to the recent Bonin Islands, Japan region earthquake which occurred on May 30, 2015 with the magnitude of 7.8. The anomalous outgoing longwave radiation (OLR) was observed on May 15, 2015, and was recorded by “NOAA 18” satellite during its “night pass.” Similarly, an abnormal infrasound spike was recorded at the Beijing station on May 17, 2015. The delay in observing anomalous infrasound waves compared to the OLR anomaly is due to these low-frequency waves traveling at low speed with the velocity range of 10–15 m/s. From the analysis of the results, it can be inferred that there is a substantial relation between parameters like OLR and infrasound waves; hence, the authors conclude that it is possible to forecast the earthquake on a short-term basis with reasonable accuracy.     

基于尼泊尔Mw7.8地震的喜马拉雅俯冲带滑坡分布规律研究

全球多数大地震发生在俯冲带地区,然而对于俯冲带地震诱发的滑坡研究并不多见。2015年4月25日尼泊尔廓尔喀县发生了Mw78地震,为喜马拉雅俯冲带近70年来的首次强震,震源机制解表明为低角度逆冲型的俯冲带地震,触发了大量滑坡、崩塌等地震次生灾害。通过遥感解译和现场调查获取2072组地震滑坡信息,揭示滑坡多数分布在海拔1000m~3000m之间,高喜马拉雅与低喜马拉雅的过渡区域,基本沿主中央逆冲断裂断裂(MCT)展布,地势落差大。早期断裂活动频繁,由中、高级变质岩和新生代浅色花岗岩变为古生代沉积岩和少量岩浆岩组成的逆冲岩席,易于发生滑坡、崩塌等地质灾害。滑坡坡度值优势分布区间为35°~40°,与中国西部地区一致,说明地震滑坡坡度分布与大的构造背景相关性较小,可能受局部地形地貌、地层岩性等因素控制。坡向值的优势分布区间为120°~200°,与水平形变场关系紧密。以尼泊尔地震滑坡为例探讨了喜马拉雅俯冲带地震滑坡的特征：滑坡点明显呈相对较宽的矩形区域展布,受深部逆冲推覆构造低倾角的断层破裂面影响较大,滑坡全部位于上盘,由于地震运动的惯性作用,在坡向与上盘逆冲方向一致的斜坡上容易诱发地震滑坡。     

Variable anelastic attenuation and site effect in estimating source parameters of various major earthquakes including M w 7.8 Nepal and M w 7.5 Hindu kush earthquake by using far-field strong-motion data

International Journal of Earth Sciences - Strong-motion records of recent Gorkha Nepal earthquake (M w 7.8), its strong aftershocks and seismic events of Hindu kush region have been analysed for...     

Spatial characteristics of landslides triggered by the 2015 M<Subscript>w</Subscript> 7.8 (Gorkha) and M<Subscript>w</Subscript> 7.3 (Dolakha) earthquakes in Nepal

High magnitude earthquakes trigger numerous landslides and their occurrences are mainly controlled by terrain parameters. We created an inventory of 15,551 landslides with a total area of 90.2 km² triggered by the 2015 M_w 7.8 (Gorkha) and M_w 7.3 (Dolakha) earthquakes in Nepal, through interpretation of very high resolution satellite images (e.g. WorldView, Pleiades, Cartosat-1 and 2, Resourcesat-2). Our spatial analysis of landslide occurrences with ground acceleration, slope, lithology and surface defomation indicated ubiquitous control of steep slope on landslides with ground acceleration as the trigger. Spatial distribution of landslides shows increasing frequency away from the Gorkha earthquake epicentre up to 130 km towards east, dropping sharply thereafter, which is an abnormal phenomenon of coseismic landslides. Landslides are laterally concentrated in three zones which matches well with the seismic rupture evolution of Gorkha earthquake, as reported through teleseismic measurements.     

New data on crustal sensitive zones and formation of precursors and postseismic responses to earthquakes

The paper summarizes twenty years of studies in crustal sensitive zones. Sensitive zones show prominent geophysical responses to stress and strain changes and high-amplitude and distant preseismic and postseismic effects. Four sensitive zones are known today in Turkmenistan, Uzbekistan, Armenia, and northeastern China, which occur at junctions of large crustal blocks. High-amplitude and distant responses are due to deformation and high strain sensitivity of geophysical parameters along block boundaries. Data from sensitive zones are used to investigate earthquake-related effects as controlled by crustal heterogeneity and nonlinearity. These effects act also outside sensitive zones and should be taken into account when interpreting precursor signals. The knowledge of sensitive zones has important implications for active deformation along block boundaries.     

Performance evaluation of the M8 algorithm to predict M7+ earthquakes in Turkey

The M8 algorithm is one of the most reliable intermediate-term middle-range earthquake prediction algorithms. The present study evaluates the ability of the M8 algorithm and its modified versions for predicting major events (M7+) in Turkey. Thirty different algorithms were developed by changing the radius of circle of investigation (CI) and the lower magnitude cutoff of the M8 algorithm. These modified algorithms were executed all over the territory of Turkey, and the results were evaluated using the error diagram. Each modified algorithm was executed for consecutive half-year intervals over a specified period of time. Subsequently, the seismic catalog was updated, and failures-to-predict ratio and the fraction of alarm were considered. Results showed that the location of areas of alarm change gradually over consecutive intervals, and no sudden changes can be observed. In addition, the annual changes of areas of alarm are not random and follow a pattern. This study also showed that the modified algorithm having a three to six annual average of events and a 393-km CI radius is an efficient algorithm for predicting the future seismic events in Turkey. This algorithm predicted six out of six target events, retrospectively, with a confidence level of 96.4 %. According to the obtained results, it will be possible to rely on this modified algorithm to predict near future earthquakes of Turkey. Furthermore, this study proves that it is possible to alter the M8 algorithm for being used in regional studies.     

Reappraisal of great historical earthquakes in the northern Chile and southern Peru seismic gaps

A critical reappraisal of great historical interplate earthquakes in the occidental margin of South America, including southern Peru and northern Chile, is carried out.A spacetime distribution of the earthquakes associated to the seismotectonics regions defined by the rupture zones of the greatest events (1868, Mw = 8.8 and 1877, Mw = 8.8) is obtained. Both regions are seismic gaps that are in the maturity state of their respective earthquake cycles. The region associated to the 1868 earthquake presents a notable seismic quiescence in the present century.     

Source zones of the catastrophic Simushir earthquakes on November 15, 2006 (M w = 8.3) and January 13, 2007 (M w = 8.1) and the deep crust structure beneath the Middle Kuril segment

The data on catastrophic earthquakes with magnitudes of 8.3 and 8.1 that occurred in the Simushir Island area on November 15, 2006, and January 13, 2007, respectively, were compared with the results of land-sea deep seismic studies by different methods (deep seismic sounding, the correlation method of refracted waves, the earthquake converted-wave method, the common mid-point) in the Central Kuril segment. The structure of the Earth’s crust and the hypocentral zones of these earthquakes were analyzed. It was established that the hypocenter of the main shock of the first earthquake was located at the bend of the seismofocal zone under the island slope of the trench on the outer side of the subsiding lithospheric plate in the rapidly rising granulite-basite (ìbasalticî) crustal layer, which, at depths of 7–15 km, replaced the granulite-gneiss layer. This was accompanied by an increase of the seismic wave velocity from 6.4 to 7.1 km/s. The focus of the second earthquake was located beneath the axis of the deep-sea trench. The aftershocks were concentrated in two bands 60–120 km wide that extend along the trench, as well as in the third zone orthogonal to the island arc. It was shown that the epicenters of the earthquakes are linked with regional faults. The main shock of the first earthquake (November 15, 2006) was interpreted as a thrust fault and the second one (January 13, 2007) was attributed to a normal fault.     

漳华龙地区地磁异常与地震对应关系分析

选取龙岩台的地磁资料,总结漳华龙地区震例,用压磁效应、感应磁效应等理论解释、分析地震与地磁异常的对应关系。结果表明,不同类型的地震,在孕育地震的不同时期,有不同的地质构造运动,产生的地磁异常也是不尽相同的。地磁异常的显著程度不仅与地震的应力降、震级、以及岩石的磁性有关,还和震源机制关系很大。     

Dynamics of the seismicity of the Kuril arc based on multivariate statistical analysis

The spatial-temporal distributions of earthquakes in the Kuril-Okhotsk region were analyzed. The events with Ms ≥ 4 from 1980 until 2009 and Ms ≥ 7 from 1910 until 2009 (20576 and 76 earthquakes, respectively) were studied. The specially developed program complex allowed us to obtain the 4-D distribution of the seismic events (along the sections, depths, temporal intervals, and energetic levels). It was shown that the seismic events obviously tend to cluster both along the surface and depth directions. The spatial-temporal analysis of the events (with Ms ≥ 4) in six five-year intervals from 1980 until 2009 has revealed a cyclic increase and decrease in the seismic activity in different time intervals and its cyclic migration from the South through the Central to the North Kuriles and back. The analysis of the strong events with Ms ≥ 7 in twenty 5-year intervals during 1910–2009 has shown that their amount significantly decreased for the last 30 years and the location of the hypocenter depths also changed (only shallow-focus earthquakes have been observed since 1975). The peaks of the seismic activity (1915–1919, 1955–1969, and 2005–2009) are separated by 35-year periods of its decrease.     

基于2001—2015年遥感数据的天山山区雪线监测及分析

基于2001—2015年MOD10A1/MYD10A1、MOD13Q1以及相关气象数据,采用积雪持续时间比率法,监测了天山山区的季节雪线高程,分析了其变化特征及影响因子。结果表明:①近15年天山山区雪线整体呈显著上升趋势,平均高程3 680 m左右,其中,北坡、伊犁河谷、南坡季节雪线的稳定性依次减弱,平均高程分别为3 620 m、3 390 m及3 820 m;空间上雪线高程呈现南高北低、东高西低的纬度地带性分布特点。②年际尺度上,气温是影响天山山区雪线高程的主控因素,呈显著正相关,南北坡与之相同,但伊犁河谷则降水是影响其变化的主控因素,呈显著负相关;季节尺度上,夏季气温、冬季降水是影响雪线高程的主控因素,降水与其呈负相关,但气温较高的地区,夏秋季降水会促进积雪融化,使雪线高程上升;月尺度上,7月气温、1月降水对其影响最明显,且存在一定的滞后反应。③天山山区雪线高程比零度层低800 m左右,两者呈较好正相关;雪线高程与NDVI（Normalized Difference Vegetation Index）呈负相关,植被覆盖较好区域,同年NDVI与雪线高程相关性较好,植被覆盖较差区域,前一年NDVI与其相关性较好。     

Probabilistic seismic risk analysis in the Taiwan area based on PGA and spectral amplitude attenuation formulas

A method for conducting a seismic hazard analysis of active faults using a fault-rupture model and a point-source model is presented. Based on a peak ground acceleration (PGA) attenuation formula, the annual probability of exceedance at a specific site is calculated. The uniform hazard spectrum is also determined based on a spectral amplitude attenuation formula. To improve the reliability of the seismic hazard analysis, a detailed study of hazard parameters is conducted and discussed. A specific site in Taiwan is chosen to illustrate the hazard analysis.