Topography of the Moho and Conrad discontinuities in the Kyushu district,Southwest Japan

The first P-arrival time data from local earthquakes are inverted for two-dimensional variation of the depths to the Conrad and Moho discontinuities in the Kyushu district, southwest Japan. At the same time, earthquake hypocenters and station corrections are determined from the data. The depths to the discontinuities are estimated by minimizing the travel time residuals of first P-arrival phases for 608 earthquakes observed at 57 seismic stations. In the land area of Kyushu, the Conrad and Moho discontinuities are located within the depth ranges of 16–18 and 34–40 km, respectively. The Conrad discontinuity is not as largely undulated as the Moho discontinuity. The depth to the Moho is deep along the east coast of Kyushu, and the deepest Moho is closely related to markedly low velocity of P wave. We regard the deepest Moho as reflecting the Kyushu–Palau ridge subducting beneath the Kyushu district, together with the Philippine Sea slab. In western Kyushu, the shallow Moho is spreading in the north–northeast–south–southwest direction in the Okinawa trough region. Based on the presence of low-velocity anomaly in three-dimensional velocity structure and seismogenic stress field of shallow crustal earthquakes, the shallow Moho is interpreted as being due to lower crustal erosion associated with a small-scale mantle upwelling in the Okinawa trough region. The velocity discontinuity undulation basically has insignificant effect on hypocenter determination of the local earthquakes, but the Moho topography makes changes in focal depths of some upper mantle earthquakes. The depth variation of the Moho discontinuity has a good correlation with the Bouguer gravity anomaly map; i.e., the shallow Moho of western Kyushu and the deep Moho of eastern Kyushu closely correlate with the positive and negative Bouguer gravity anomalies, respectively.     

Influence of fluids on deep crustal Jabalpur earthquake of 21, May 1997: Geophysical evidences

We present the geophysical evidences on the role of fluids for generation of the lower crustal Jabalpur earthquake (21 May 1997, mb 6.0, Mw 5.8), in the mid-continental fracture zone of the Indian Peninsular Shield. With a focal depth of 35 km, it indicates a high angled (< 62^∘ enclosed with maximum principal stress direction) reverse fault with small component of left-lateral strike slip in the lower crust. The Son-Narmada-Tapti (SONATA) magalineament, during the past two centuries, has experienced about 25 moderate to strong earthquakes; two of which namely the Son Valley (1927, M 6.5) and Jabalpur (21 May 1997) were disastrous. Historical earthquakes and recent earthquake swarms indicate a moderate to high seismicity in SONATA belt that is due to high strain accumulation, flexuring of the crust and neotectonic movements of the faults in the rift zones. By analyzing geophysical parameters such as Zero-Free air-based (ZFb) gravity anomalies (∼ −10 to –30 mGals), heat flow values (45–47 mWm⁻²), magneto-telluric values (1- Ohm m), strain rate (1.5 × 10⁻⁸) and failure stress conditions, we identify plausible causative factors for the occurrence of lower crustal earthquake in this region Fluids, due to dehydration of serpentinite in the lower crust, are suggested to be present in the earthquake source zone. The estimated pore-fluid factor for the Jabalpur earthquake (λ _v ) is 0.95. The diffusion of pore-pressure relaxation, represented as pressure perturbation generated by coseismic stress change was seen in the form of swarm activity two years prior to the Jabalpur earthquake. We suggest the existence of a deep pre-fractured zone with low shear stress (τ = 15–18 MPa) that indicates the presence of fluid filled fractured mafic material in the felsic crust, in critical state of unstable failure condition, and also fluid driven migration of swarm activity before the Jabalpur earthquake.     

据地壳介质非均匀性判断郯庐断裂带鲁苏段未来大震位置

从大尺度和小尺度两方面研究郯庐断裂带苏鲁段地壳介质非均匀性。使用地震波数据,研究了郯庐断裂带苏鲁段地壳速度结构的非均匀性,单位虚波Q_mps的非均匀性,地壳介质泊松比的非均匀性,反映地壳介质小尺度非均匀性的分层κ值和y值。计算了1668年郯城8 1/2级地震震源区长度和沿断裂带的震源区边界,根据地震构造和地震活动性确定断裂的闭锁段,地震应力的积累单元和调整单元。对比1668年郯城8 1/2级地震的地壳介质状况,将各种非均匀性参数综合分析,结果表明,各种参数指向一致,未来大震的可能区域是33°-34.5°N,118°-118.8°E的北北东向区域,震级可达8级。     

2014年新疆于田MS7.3地震序列重定位及其发震构造初步研究

2014年2月12日在新疆于田县发生了M_S7.3地震,主震前一天在震区发生了M_S5.4前震,震后余震活动频繁,由于震区台站十分稀疏和不均匀、地壳速度结构复杂,台网常规定位结果精度有限,很难从中获得序列的空间分布特征和活动趋势的正确认识.本文首先利用位于震区附近的于田地震台5年记录的远震波形数据,采用接收函数方法研究了震区附近的地壳结构,建立了震源区的地壳速度模型.在此基础上,联合震相到时和方位角对2014年于田M_S7.3地震序列(从2014年02月11日-2014年04月30日,共计577次地震)进行了重新绝对定位.结果显示,(1) 重定位后的前震和主震震中位置明显向地表破裂带及其附近的阿尔金分支断裂(南肖尔库勒断裂和阿什库勒-肖尔库勒断裂)靠近,两者相距5.4 km,主震位置为36.076°N、82.576°E,震源深度为22 km, 前震位置为36.055°N、82.522°E,震源深度为19 km;(2) 本文重定位结果显示,余震序列沿NEE-SWW展布,优势分布长度约73 km、宽度约16 km,平均震源深度为14.8 km,其中77%的余震分布在地表破裂带的西南端,这部分余震中少数沿阿什库勒-肖尔库勒断裂分布,绝大多数沿北东东向的南肖尔库勒断裂分布,位于地表破裂带东北端的余震沿阿什库勒-肖尔库勒断裂分布,但发生在地表破裂带的余震极少;重定位后,位于地表破裂带西南侧的震中分布由台网目录的近南北向变为北东向,与地表破裂带、南肖尔库勒断裂和阿什库勒-肖尔库勒断裂走向一致;(3) 沿重定位剖面的地震分布,可推断位于地表破裂带西南段的南肖尔库勒断裂与位于北东段的阿什库勒-肖尔库勒断裂倾向反向,南肖尔库勒断裂的倾向为SE,阿什库勒-肖尔库勒断裂的倾向为NW,这与本次地震野外考察得到的断裂性质一致.综合重定位结果、地表破裂带分布、震源机制解、南肖尔库勒断裂和阿什库勒-肖尔库勒断裂的性质认为,2014年于田M_S7.3地震的发震构造为阿尔金断裂西南尾段的两条分支断裂——南肖尔库勒断裂和阿什库勒-肖尔库勒断裂.     

考虑到时误差的地震定位算法及其在四川地区2001-2008年地震定位的应用

精确的地震位置对于地震活动性、地震层析成像和地壳应力场反演具有相当重要的意义,对于地震速报也具有重要的应用价值。将观测到时的不确定性、台站高程、地震震源深度进行约束的同时,根据反演理论给出了地震震源位置精确估计和误差估计的方法。该算法联合考虑Pg波、Sg波、Pn波和Sn波的到时进行反演,数据量的增加可以增强地震位置的准确性,并可同时应用于地方震和区域地震。采用模拟数据对该地震定位算法进行检验发现,该算法在观测数据的不确定性不等时明显优于其他方法。将该算法应用于四川地区2001-2008年间的地震定位,得到的地震位置更加符合地震的丛集性并集中于断裂带附近。这些结果为四川地区的地震活动性、断层构造以及地震层析成像研究打下了基础,并且为汶川地震之前的地震活动前兆研究也提供了有益帮助。     

Earthquake relocation in the Central Alborz region of Iran using a non-linear probabilistic method

In this study, we calculate accurate absolute locations for nearly 3,000 shallow earthquakes (≤20 km depth) that occurred from 1996 to 2010 in the Central Alborz region of northern Iran using a non-linear probabilistic relocation algorithm on a local scale. We aim to produce a consistent dataset with a realistic assessment of location errors using probabilistic hypocenter probability density functions. Our results indicate significant improvement in hypocenter locations and far less scattering than in the routine earthquake catalog. According to our results, 816 earthquakes have horizontal uncertainties in the 0.5–3.0 km range, and 981 earthquakes are relocated with focal-depth errors less than 3.0 km, even with a suboptimal network geometry. Earthquake relocated are tightly clustered in the eastern Tehran region and are mainly associated with active faults in the study area (the Mosha and Garmsar faults). Strong historical earthquakes have occurred along the Mosha and Garmsar faults, and the relocated earthquakes along these faults show clear north-dipping structures and align along east–west lineations, consistent with the predominant trend of faults within the study region. After event relocation, all seismicity lies in the upper 20 km of the crust, and no deep seismicity (>20 km depth) has been observed. In many circumstances, the seismicity at depth does not correlate with surface faulting, suggesting that the faulting at depth does not directly offset overlying sediments.     

Temporal migration of earthquakes in Koyna–Warna (India) region by pore-fluid diffusion

Continuous occurrences of several thousands of earthquakes in Koyna–Warna region since the initial impoundment (1962) of the Koyna reservoir has attracted the attention of seismologists all over the world to know the exact earthquake physical processes involved. The area has been a site for reservoir-triggered earthquakes for the last four and half decades. Major bursts of seismic activity occurred during 1967, 1973, 1980, 1993, and 2000 and recently in 2005 with magnitudes exceeding 5.0 in the region. A notable southward migration of seismicity has been observed following the impoundment of another reservoir, the nearby Warna reservoir. All the mainshocks suggest that the significant southward migration might be due to pore-pressure diffusion. We have divided the entire period from 1967 to 2007 in several sequences starting by a mainshock of M >5. Each sequence is critically analyzed in terms of triggering by the diffusion process through the fractured medium. The pore-fluid diffusion tensor D for each sequence is estimated based on Darcy’s law. The direction of temporal migration of seismicity of each sequence except 1980 is correlated well with the eigenvectors of diffusion. The fluid flow eigenvectors are constrained with one of the strike directions of the focal mechanisms. The frequency magnitude distribution shows the b value to vary from 0.5 to 1.2. Spatial distribution of the b value further indicates that the area along the major faults is more prone to future earthquake.     

Earthquake deformation in the northwestern Sierras Pampeanas of Argentina based on seismic waveform modelling

We investigate the seismic properties of modern crustal seismicity in the northwestern Sierras Pampeanas of the Andean retroarc region of Argentina. We modelled the complete regional seismic broadband waveforms of two crustal earthquakes that occurred in the Sierra de Velasco on 28 May 2002 and in the Sierra de Ambato on 7 September 2004. For each earthquake we obtained the seismic moment tensor inversion (SMTI) and tested for its focal depth. Our results indicate mainly thrust focal mechanism solutions of magnitudes M_w 5.8 and 6.2 and focal depths of 10 and 8 km, respectively. These results represent the larger seismicity and shallower focal depths in the last 100 years in this region. The SMTI 2002 and 2004 solutions are consistent with previous determinations for crustal seismicity in this region that also used seismic waveform modelling. Taken together, the results for crustal seismicity of magnitudes ≥5.0 in the last 30 years are consistent with an average P-axis horizontally oriented by an azimuth of 125° and T-axis orientation of azimuth 241° and plunge 58°. This modern crustal seismicity and the historical earthquakes are associated with two active reverse faulting systems of opposite vergences bounding the eastern margin of the Sierra de Velasco in the south and the southwestern margin of the Sierra de Ambato in the north. Strain recorded by focal mechanisms of the larger seismicity is very consistent over this region and is in good agreement with neotectonic activity during the last 11,000 years by Costa (2008) and Casa et al. (in press); this shows that the dominant deformation in this part of the Sierras Pampeanas is mainly controlled by contraction. Seismic deformation related to propagation of thrusts and long-lived shear zones of this area permit to disregard previous proposals, which suggested an extensional or sinistral regime for the geomorphic evolution since Pleistocene.     

Probabilistic seismic hazard assessment for Thailand

A set of probabilistic seismic hazard maps for Thailand has been derived using procedures developed for the latest US National Seismic Hazard Maps. In contrast to earlier hazard maps for this region, which are mostly computed using seismic source zone delineations, the presented maps are based on the combination of smoothed gridded seismicity, crustal-fault, and subduction source models. Thailand’s composite earthquake catalogue is revisited and expanded, covering a study area limited by 0°–30°N Latitude and 88°–110°E Longitude and the instrumental period from 1912 to 2007. The long-term slip rates and estimates of earthquake size from paleoseismological studies are incorporated through a crustal fault source model. Furthermore, the subduction source model is used to model the megathrust Sunda subduction zones, with variable characteristics along the strike of the faults. Epistemic uncertainty is taken into consideration by the logic tree framework incorporating basic quantities, such as different source modelling, maximum cut-off magnitudes and ground motion prediction equations. The ground motion hazard map is presented over a 10 km grid in terms of peak ground acceleration and spectral acceleration at 0.2, 1.0, and 2.0 undamped natural periods and a 5% critical damping ratio for 10 and 2% probabilities of exceedance in 50 years. The presented maps give expected ground motions that are based on more extensive data sources than applied in the development of previous maps. The main findings are that northern and western Thailand are subjected to the highest hazard. The largest contributors to short- and long-period ground motion hazard in the Bangkok region are from the nearby active faults and Sunda subduction zones, respectively.     

Role of crustal fluids in triggering the West Bohemia/Vogtland earthquake swarms: Just what we know (a review)

We summarise the results of seismological studies related to triggering mechanisms, driving forces and source processes of the West Bohemia/Vogtland earthquake swarms with the aim to disclose the role of crustal fluids in the preparation, triggering and governing of the swarms. We present basic characteristics distinguishing earthquake swarms from tectonic mainshock-aftershock sequences and introduce existing earthquakes swarm models. From the statistical characteristics and time-space distribution of the foci we infer that self-organization is a peculiarity of West Bohemia/Vogtland swarms. We discuss possible causes of the foci migration in these swarms from the viewpoint of co-seismic and/or post-seismic stress changes and diffusion of the pressurized fluids, and we summarize hitherto published models of triggering the 2000-swarm. Attention is paid to the source mechanisms, particularly to their non-shear components. We consider possible causes of different source mechanisms of the 1997-and 2000-swarms and infer that pure shear processes controlled solely by the regional tectonic stress prevail in them, and that additional tensile forces may appear only at unfavourably oriented faults. On data from the fluid injection experiment at the HDR site Soultz (Alsace), we also show that earthquakes triggered by fluids can represent purely shear processes. Thus we conclude that increased pore pressure of crustal fluids in the region plays a key role in bringing the faults from the subcritical to critical state. The swarm activities are mainly driven by stress changes due to co-seismic and post-seismic slips, which considerably depend on the frictional conditions at the fault; crustal fluids keep the fault in a critical state. An open question still remains the cause of the repeatedly observed almost simultaneous occurrence of seismic activity in different focal zones in a wider area of West Bohemia/Vogtland. The analysis of the space-time relations of seismicity in the area between 1991 and 2007 revealed that during a significant part of this time span the seismicity was switching among distant focal zones. This indicates a common triggering force which might be the effect of an increase of crustal-fluid pore-pressure affecting a wider epicentral region.     

The deep structure of the Kulu earthquake-generating zone in the upper Kolyma highland from geophysical data

We measured and interpreted 30 physical magnetotelluric sounding sites using an SGS-E station and 20 km of electrical profiling observations using SDVR-4M instrumentation. We constructed a map of seismicity, an interpretation map, and four geoelectric sections, which give an idea of the deep structure for the Kulu earthquake-generating zone. A general geoelectric upper crustal model was developed for the zone down to depths of 20–22 km. Three nearly vertical conductive volumes were identified (thickness 3–5 km, depth 10–22 km), which provide the positions of seismically active deep-seated faults that pinpoint the Kulu earthquake-generating zone. The preliminary boundary of the zone was determined. It was found that earth-quake epicenters are confined to lithosphere volumes with increased concentrations of conductive layers and zones.     

A near-bottom geophysical traverse of the Reykjanes Ridge

We report here the results of a near-bottom geophysical survey of the Reykjanes Ridge, a mid-ocean ridge that is oriented obliquely to the perpendicular spreading direction. From a combination of the bathymetric profiles, side-scan sonar data, and regional bathymetric maps we infer that the present center of spreading is made up of a number of N15°E-trending en echelon ridge segments in the southern half of our survey area. Insufficient data prevent the identification of the spreading pattern in the northern half. The side-scan records show that the ridge flanks are highly fractured by inward-facing faults displaced 40 m or less and trending in a N21°E direction. The lack of side-scan features parallel to the spreading direction except in the southernmost portion of the survey area suggests that the ridge segments are not connected by transform faults in the usual sense. Although the mechanism by which en echelon ridge segments can be maintained during sea-floor spreading over time is unclear, similar patterns of crustal accretion have been reported on Iceland. It appears that the accretionary processes along the Reykjanes Ridge are more related to those of Iceland than to those of typical mid-ocean ridges.     

四川二滩水电站围堰期间诱发地震的初步研究

二滩水电站位于四川雅砻江下游，是目前西南地区正建设的规模最大的水电枢纽工程。本文综合了区域地震地质、历史地震和库区水文地质条件，概述了该区域的孕震构造背景；使用二滩遥测地震台网自１９９１年７月正式运转以来积累的数字化记录资料，计算卫Ｐ波和Ｓ波的速度结构、地壳介质Ｑ、应力降；在此基础上，引用了数值性能极好的先进技术，对库区地震进行震源位置和深度的精确确定，由本文描画的地震空间分布立体图象，讨论了库区     

汶川8.0级地震对鄂尔多斯块体西南缘断裂体系影响的数值模拟

利用有限元方法及静态位移解理论,采用前人反演的汶川8.0级地震破裂过程时空参数,定量计算分析汶川地震对鄂尔多斯块体西南缘断裂体系的影响.数值计算表明,具逆冲右旋性质的汶川地震,在汶川-宝鸡-线以东产生顺时针的位移扰动场,以西产生逆时针的位移扰动场,这与该分界两侧附近的活断层整体走滑方向相一致.水平剪切应力场的局部极值区...     

Normal faulting mechanisms in the Western Desert of Egypt

Egypt is recognized as a moderate seismicity region where earthquakes are distributed within several active regions. Owing to sparse distribution of both seismicity and seismic stations, mostly moderate-size Egyptian earthquakes were recorded by regional stations. One of such cases is the moderate-size earthquakes of moment magnitudes greater than 4.0 which struck the Western Desert of Egypt in 1998 and 1999. These events are the first instrumentally recorded earthquakes occurring in the area. In the present study, the source mechanism for these earthquakes was estimated using the waveform data recorded from one of the very broadband MedNet seismograph stations and polarities from the national short-period seismographs. An iterative technique was applied to find the best-fit double-couple mechanism by a grid search over strike, dip and rake. Regional synthetic seismograms were calculated by using f–k integration in the frequency range of 0.03–0.1 Hz. A crustal structure fitted to surface wave dispersion curves was used to compute Green’s function. Focal depths were determined through the grid search method for a range of source depths. Our results show a normal faulting mechanism with minor strike-slip component. The NNW trend has been chosen as a preferred rupture plane in consistence with surface and subsurface faults and microearthquake seismicity in the epicenteral area as well.     

Earthquake relocation and 3-dimensional crustal structure of P-wave velocity in cen-tral-western China

IntroductionUnderstandingthemechanismofcontinentalearthquakesisveryimportantforseismichaz-ardpreventionandearthquakeprediction.Themodernseismotectonictheoryandtheideaofearthquakepredictionaredevelopedmainlyfromthestudiesoninterplateearthquakes,whicharedifficulttoexplainthephenomenaofintraplateearthquakes,suchasthecontinentalearthquakesoccurredinChinesemainland.Whiletheinterplateearthquakesoccurredalongtheplatebounda-ries,theintraplateearthquakesdistributediffuselyintheinterioroftheplates.Thus…     

Calibration of the Tibetan Plateau Using Regional Seismic Waveforms

We use the recordings from 51 earthquakes produced by a PASSCAL deployment in Tibet to develop a two-layer crustal model for the region. Starting with their ISC locations, we iteratively fit the P-arrival times to relocate the earthquakes and estimate mantle and crustal seismic parameters. An average crustal P velocity of 6.2–6.3 km/s is obtained for a crustal thickness of 65 km while the P velocity of the uppermost mantle is 8.1 km/s. The upper layer of the model is further fine-tuned by obtaining the best synthetic SH waveform match to an observed waveform for a well-located event. Green's functions from this model are then used to estimate the source parameters for those events using a grid search procedure. Average event relocation relative to the ISC locations, excluding two poorly located earthquakes, is 16 km. All but one earthquake are determined by the waveform inversion to be at depths between 5 and 15 km. This is 15 km shallower, on average, than depths reported by the ISC. The shallow seismicity cut-off depth and low crustal velocities suggest high temperatures in the lower crust. Thrust faulting source mechanisms dominate at the margins of the plateau. Within the plateau, at locations with surface elevations less than 5 km, source mechanisms are a mixture of strike-slip and thrust. Most events occurring in the high plateau where elevations are above 5 km show normal faulting. This indicates that a large portion of the plateau is under EW extension.     

RELOCATION OF THE BACKGROUND SEISMICITY AND INVESTIGATION ON THE BURIED ACTIVE FAULTS IN SOUTHEASTERN CHINA

Most of the regions in southeastern China are covered by thick Cenozoic sediments, or are the mountainous areas, so it is difficult to find and locate the active faults using the conventional geologic methods. The precisely relocated background seismicity in the seismically active region can be used to identify the buried active structure. In this paper, we investigated the relationship between regional tectonics and background seismicity, and interpreted the possible buried active faults in southeastern China using the relocated background seismicity. We relocated the background seismicity occurring in the region from 106°E to 122°E and from 22°N to 35°N between 1990 and 2014 using the doubble difference earthquake location algorithm. More than 51000 small earthquakes were relocated. In general, the relocated background seismicity corresponds well to the tectonics, showing the zonation features with typical seismicity pattern in each tectonic regime. It is observed that in the weakly active tectonic regime, the seismicity distributes dispersely or even scarcely, while in the strongly active tectonic region, the seismicity is highly clustered and organized to lineation pattern showing the same direction as the strike of the dominating fault zone. We interpreted the buried active faults using the lineation of seismicity. The inferred active faults are observed in the southeast coast region, the northwest Guangxi Province, the southeast boundary region of the Sichian Basin, and around the Huoshan Fault, many of which were not found by previous studies. The relocated hypocentral depth varies greatly in southeastern China. The shallowest earthquakes between 0 and 15km mainly distribute in the central region, indicating that the brittle deformation process only occurred in the upper crust, while the middle and lower crust are to be half-ductile and ductile deformation. There are earthquakes occurred in lower crust in the southeast coast region. The maximum depths distribute in the southeast boundary region of the Sichuan Basin, some are greater than 40km, indicating that the crust depth is larger than other places and the lower crust still sustains brittle deformation, which corresponds to the lower geothermal value and high crustal strength.     

SEISMO-GEOLOGICAL SIGNATURES FOR IDENTIFYING M≥7.0 EARTHQUAKE RISK AREAS AND THEIR PREMILIMARY APPLICATION IN MAINLAND CHINA

High-magnitude earthquake refers to an earthquake that can produce obvious surface ruptures along its seismogenic fault and its magnitude M is at least equal to 7.0. Prediction and identification of locations, where the high-magnitude earthquakes will occur in potential, is one of the scientific goals of the studies on long-term faulting behavior of active faults and paleo-earthquakes, and is also the key problem of earthquake prediction and forecast. The study of the geological and seismological signatures for identifying M≥7.0 earthquake risk areas and their application is an important part of seismic prediction researches. It can not only promote the development of earthquake science, especially the progress of earthquake monitoring and forecasting, but also be positive for earthquake disaster prevention and effective mitigation of possible earthquake disaster losses. It is also one of the earthquake science problems which the governments, societies and the scientific communities are very concerned about and need to be addressed. Large or great earthquakes, such as the 2008 Wenchuan earthquake(M8.0), the 2010 Yushu earthquake(M7.1), the 2013 Lushan earthquake(M7.0)and the 2015 Gorkha earthquake(M_W7.8), have unceasingly struck the Qinghai-Tibet Plateau and its surrounding areas, which have been attracting attention of a large number of geoscientists both at home and abroad. Owing to good coverage of the seismic networks and GPS sations, a lot of high-quality publications in seismicity, crustal velocity structure, faulting beihavior have been pressed, which gives us a good chance to summarize some common features of these earthquakes. In this paper, seismogenic structural model of these earthquakes, faulting behavior of seismogenic faults, crustal mechanical property, recent straining environment and pre-earthquake seismicity are first analyzed, and then, five kinds of common features for the sismogenic faults where those earthquakes occurred. Those five kinds of commom features are, in fact, the geological and seismological signatures for identifying M≥7.0 earthquake risk areas. The reliability of the obtained sigatures is also discussed in brief. At last, based on the results of 1:50000 active fault mapping, and published seismic tomography and fault-locking studies, an experimental identification of the risk areas for the future large/great earthquakes in the North China and the Qinghai-Tibet Plateau is conducted to test the scientificity and applicability of these obtained sigantures.     

Relation of surface movements in West Bohemia to earthquake swarms

GPS observations in the Western Bohemia/Vogtland earthquake swarm region revealed indications of horizontal displacements of low amplitude, and no clear long-term trend in 1993–2007. On the other hand, in 1998–2001 there was relatively significant active movement along NNE-SSW oriented line that we called the “Cheb-Kraslice GPS Boundary” (ChKB), identical with an important limitation of earthquake activity. The most impressive were dextral (right-lateral) movements in the 1998–1999 period followed by reverse sinistral (left-lateral) movements in 1999–2000 that correlate with prevailing motion defined by fault plane solutions of the Autumn 2000 earthquake swarm. Before the February 2004 micro-swarm, two points located on opposite sides of the Mariánské Lázně fault showed extension in the order of about 7 mm in the same NNE-SSW direction of ChKB. The new NOKO permanent GPS station in Novy Kostel showed the peak-to-peak vertical changes up to 10 mm before and during the February 2007 micro-swarm. Annual precise levelling campaigns in the local network around Novy Kostel revealed regular vertical displacements during the 1994, 1997 and 2000 earthquake swarms. The points around the Novy Kostel seismological station showed uplift during the active periods, including the micro-swarm February 2004. However, no such indication was observed on levelling points in the period of the February 2007 swarm. Long-term vertical displacements depend on the same direction NNE-SSW (ChKB) as the GPS displacements. Both geodetic techniques have revealed oscillating displacements, GPS horizontal, and levelling vertical, rather than any long-term trends in the study period 1993–2007. The displacements exhibited significant spatial and temporal relation to tectonic activity (earthquake swarms) including their coincidence with the seismologically determined sense of motion along the fault plane during earthquakes.