Vertical Displacements in the Nový Kostel Seismoactive Area

Since 1994 annual campaigns of precise levelling have been performed on the network established in the surroundings of Nový Kostel. The network covers the most dynamic part of the West Bohemia seismoactive region with a total of 70 points in 1999. The measurements are connected to a reference point of the national levelling system and to our GPS-gravity network. It was proved by the error and confidence level of the data that small displacements of three and more millimetres can be recognised. The data analysis showed that all points could be divided into several groups according to temporal changes of height. Mutual comparison of these changes enabled to detect both general and very local short-term movements. It appeared that, in general, the involved part of the mountain block is subsiding relative to the Cheb basin. This is in contradiction to the recent uplift of the Kruné hory Mts. The correlation between vertical displacements and earthquake swarms was examined with the conclusion that during a swarm period the movements have special homogeneous pattern, contrary to inter-periods. The division line of different displacements (a fault zone) for the swarms 1994 and 1997 was determined.     

Refined Locations of The Swarm Earthquakes In The Nový Kostel Focal Zone and Spatial Distribution of The January 1997 Swarm In Western Bohemia,Czech Republic

In order to improve the accuracy of the spatial distribution of earthquake foci in the principal Novy Kostel focal zone, refined focal locations of about 1500 micro-earthquakes of the 1991 – 1997 period were determined using the relative Master-Event location method. To estimate the reduction in the scatter of located hypocentres, the results were compared with those obtained by routinely used FASTHYPO method and cluster analysis (the nearest-neighbour method) was applied to the located foci to evaluate the spatial distribution of the foci. Based on the results of refined location and of the cluster analysis, a concept of seismic energy release in space and time in the main focal zone was developed. Especially the January 1997 earthquake swarm was studied in detail: 946 events were located with the Master-Event location method, and the dimensions and geometry of focal clusters were determined. Type analysis was applied to waveforms to divide approximately 800 located events into eight multiplet groups to each of which a characteristic source mechanism was assigned. The spatial distribution of the foci as well as of the eight types of source mechanisms was revealed in this way and also the planes fitting the clusters of foci with two predominant source mechanisms were determined fairly well.     

Study of the Seismicity of Strong Earthquakes in the Yunnan Area

INTRODUCTIONYunnanis located in the east margin of the collision zone between the India Plate and theEurasian Plate on the Chinese Continent , where crustal movement is violent and moderate-strongearthquakes are frequent withlarge magnitudes and wide distributions .It is also a place of particularinterest to geo-science researchers both at home and abroad. Since 1970 , 8 earthquakes withmagnitude 7·0 have occurred here .It is a perfect site to study seismicity.Whether or not seismicit…     

Comment on the “Analysis of the State of Stress During the 1997 Earthquake Swarm in Western Bohemia” by A. Slancová and J. Horálek (Studia geoph. et geod. 44(2000), 272–291)

Studia Geophysica et Geodaetica -     

Reply to Comment by V. Vavryčuk on “Analysis of the State of Stress During the 1997 Swarm in the Western Bohemia” by A. Slancová and J. Horálek

Studia Geophysica et Geodaetica -     

Temporal variations of focal mechanisms in the Novy Kostel focal zone (Vogtland/NW-Bohemia)—comparison of the swarms of 1994, 1997 and 2000

The seismicity in the Vogtland/NW-Bohemia region is mainly characterized by the occurrence of earthquake swarms. A key to a better understanding of the reasons of earthquake swarms can be provided by focal mechanism investigations. Here we present focal mechanisms for 12 of the strongest events (M_L⩾3.0) for the new swarm of 2000. With more than 10,000 events and magnitudes up to 3.7 the new swarm is the most prominent one since the big swarm in 1985/1986. The focal mechanisms of the swarm 2000 show different styles of faulting, namely strike-slip, normal and reverse faulting. There are indications for systematic temporal variations in the dislocation type. A comparison with the mechanisms of the preceding swarms of 1985/1986, 1994 and 1997 which all took place at the same location shows similarities in the faulting types and orientations of the nodal planes for the swarms of 1985/1986, 1994 and 2000. However, the focal mechanisms of 1997 do not fit into the scheme of the others. The focal mechanisms have also been used to determine the regional stress field. It turned out that the stress field in the Vogtland/NW-Bohemia region does not substantially differ from the known stress field in West and Central Europe. It is a strike slip regime with a SE–NW directed σ₁-axis and a NE–SW directed σ₃-axis.     

On Epicentral Location of the 1216 Mahu Earthquake in Leibo County, Sichuan Province

A query regarding the now commonly accepted epicentral location of the 1216 Mahu earthquake in Leibo County, Sichuan Province is proposed after examination of local historical records of earthquakes, field investigation of the Mahu barrier lake, study of geological environment for the earthquake and the available data then a relocation of the earthquake epicenter is suggested in the paper.     

Prediction of Subtle Thin Gas Reservoir in the Loess Desert Area in the North of Ordos Basin

For thin gas reservoir of low-porosity and low-permeability in the loess desert area, a suite of lateral reservoir prediction techniques has been developed by Changqing Oil Company and the excellent effects achieved in exploration and exploitation in the areas such as Yulin, Wushenqi,Suligemiao, Shenmu etc., so that the Upper Paleozoic gas reserve has been stably increasing for eight years in Changqing Oilfield. The paper analyzed the effects and experience of the application of these techniques in detail.     

Study on the Source Parameters of Earthquakes in the Middle Eastern Area of North Tianshan in Xinjiang

INTRODUCTIONThe study of source parameters is usually based oninversionfromobservational seismic waveformdata.Seismic wave affected bygeometric spreading,inelastic attenuation,scatteringandsite effects ofthe mediumontheir way fromsource to station.Therefo…     

Application Effect of CEMP in the Foreland Basin on the Western Edge of Ordos

Foreland basins on the western edge of Ordos are characterized by typical loess geomorphologic features. Its surface is severely cut, and its underground geological structures are complicated.Making use of the advantage of CEMP in exploration in frontland as well as successful multi-year exploration experiences in West China, we first employed the CEMP method to conduct exploration on the western edge of the Ordos basin and its surrounding areas. The practices proved that rich and reliable geological results have been achieved with the CEMP method in complicated areas covered with loess. This can provide important evidence for researching the contact relationship among basins and mountains, structural feature of target layers and predict favourable areas.     

Modelling of Elastic Stress Field of the Earth’s Crust in Central Asia Based on the Orientations of Principal Stress Axes

Izvestiya, Physics of the Solid Earth - In this work, we perform reconstruction of elastic stress fields by employing discrete data on the principal directions of the stress tensor in Central Asia....     

Investigation of Fine Velocity Structure of the Basement Layer of the Shallow Crust in Western Yunnan Region

In this paper the authors have discussed the results of investigation of fine velocity structure in the basement layer of the Simao-Zhongdian DSS profile in western Yunnan region.The depth of upper Pz interface of the basement layer is about 0-3.5 km,and the depth of the lower P1 interface is 11.0-17.0 km.The velocity of the basement layer on the southern side of the Jinhe-Erhai deep fault is 5.70-6.30 km/s,and has increased to 6.30-6.50 km/s on the northern side.Their transitional zone is situated near Jianchuan County.Along the profile some localities,where the faults cut across the lateral variation of Pz interface velocity,are quite obvious in addition to the variation in depth.The velocity isopleths are relatively sparse in the southern region of JYQ S.P.(shot - point),near the DC S.P.,and in the south ZT S.P.The magma has apparently risen up along the deep faults to the upper crust in these localities,forming a large intrusive rock zone in the basement layer.In Jinggu region the basaltic magma has     

Seasonal Variations in the b-Value of the Reservoir-Triggered Seismicity in the Koyna–Warna Region,Western India

Izvestiya, Physics of the Solid Earth - Abstract—The analysis of the local earthquake catalog revealed fine features in the behavior of seasonal components of induced seismicity in the...     

Magnitudes and time distribution of the swarm earthquakes August–November 2000 in NW Bohemia

During the earthquake swarm in the north-western part of the Czech Republic which happened between August and November 2000 more than 10 500 single events have been recorded at the station Wernitzgruen (WERN), located in the Vogtland (Germany) at about 13 km hypocentral distance. Most of the events were weak and followed each other so closely in time that they could not be identified at more distant stations in Middle Europe. A procedure to determine magnitudes of very small events from recordings in short distances is realized and discussed. The development over time of the seismic activity shows the typical pattern of previous earthquake swarms in this region consisting of multiple swarm episodes. For the first time, however, it is analysed using the time intervals between successive events. However, no new and reproducible patterns were found which could be useful for prognostics of future swarm activities.     

On the Dynamics of the Seasonal Components of Induced Seismicity in the Koyna–Warna Region,Western India

The spatial and time dynamics are analyzed for the seasonal components of induced seismicity in the Koyna–Warna region of Western India. The peculiarities of the variations in these components are compared to the changes in the local tectonic regime inferred from the focal mechanism data of the earthquakes. Based on this, the hypotheses about the probable nature of the dynamics in the seasonal components of seismicity are suggested. It is noted that the variations in the seasonal seismic activity after the impoundment of the Koyna reservoir in the north are caused by the spatial migration of the induced seismicity and activation of the normal faults in the south. It is hypothesized that the process of fracture migration from the north to the south at this stage advanced the diffusion of the fluid from the Koyna reservoir, and as the water front reached the southern zone of normal faulting, this caused reactivation of the seasonal seismicity. An explanation is suggested for the stronger response of the seasonal activity in the region of Warna reservoir compared to the Koyna area: in contrast to Koyna, filling the Warna reservoir was geographically close to the area of activated seismicity. It is shown that the localization and sizes of the areas of the instantaneous and delayed components in the seasonal activity of the induced seismicity are determined by the localization and sizes of the areas of high stresses created by the increase in the pore pressure in highly permeable fault zones.     

Visibility Graph Analysis of the 2003–2012 Earthquake Sequence in the Kachchh Region of Western India

A visibility graph (VG) is a rather novel statistical method in earthquake sequence analysis; it maps a time series into networks or graphs, converting dynamical properties of the time series into topological properties of networks. By using the VG approach, we defined the parameter window mean interval connectivity time <T_c>, that informs about the mean linkage time between earthquakes. We analysed the time variation of <T_c> in the aftershock-depleted catalogue of Kachchh Gujarat (Western India) seismicity from 2003 to 2012, and we found that <T_c>: i) changes through time, indicating that the topological properties of the earthquake network are not stationary; and, ii) appeared to significantly decrease before the largest shock (M5.7) that occurred on March 7, 2006 near the Gedi fault, an active fault in the Kachchh region.     

Wavelet analysis of paleomagnetic data: 4. Characteristic short times (0.4–4.5 ky) of variations in the elements of the geomagnetic field during the early Jaramillo reversal and in the stationary field during the Matuyama and Jaramillo chrons (Western Turkmenia)

The geomagnetic variations with characteristic times ranging from 0.4 to 15 ka are shown to be largely stochastic. Variations with different characteristic times appear during different time intervals and reflect accelerating and decelerating processes. The variations do not exhibit any predominant times. At the same time, almost periodic variations in the lithological characteristics are clearly seen in the wavelet diagrams of the parameters that reflect the changes in the composition (quantitative and qualitative) of ferrimagnetic material; i.e., the changes in the conditions of sedimentation related to climate variations. The variations with periods of 5, 8.5, and 13 ka are concurrent with the similar variations in the paleomagnetic data, while the variations with a period of 3.5 ka are only observed in the magnetic parameters. We suggest that the first mentioned oscillations reflect the changes of the external (relative to the Earth) origin, whereas the changes with a period of 3.5 ka are caused by some terrestrial factors.     

Geochronological Significance of the Post-Orogenic Mafic- Ultramafic Rocks in the Hongqiling Area of Jilin Province, Northeast China

INTRODUCTIONThe mafic-ultramafic complexesinthe Hongqilingarea were emplacedintothe metamorphic rocksof the Hulan Group. Age determination of the intrusion and metamorphism of the Hulan Groupmetamorphic rocks is crucial for the study of petrogenesis and evolution, orogenesis and itsdevelopment of the region. However ,so far it has been difficult to determine the geochronology ofmafic-ultramafic rocks inthe area ,thusthe age obtainedfromprevious data hadto be used.Inrecentyears ,withthe …     

Analysis of the liquefaction phenomena in the village of Vittorito (L��Aquila)

This paper describes a case-history of liquefaction occurred near the village of Vittorito after the April 6, 2009 L’Aquila earthquake (moment magnitude M_w = 6.3), approximately 45 km far from the epicentre. In the document, first, an estimation of the seismic motion in the area has been made. Thereafter, the performed geotechnical investigation is described, followed by the application of some fast assessment criteria for the occurrence of liquefaction, recently proposed by the new Italian Building Code. A careful assessment of all the parameters involved in conventional Seed and Idriss (1971) liquefaction analyses is considered. The cyclic resistance ratio CRR is evaluated by cone penetration tests CPT and by in situ seismic dilatometer tests SMDT; in the latter case CRR is evaluated by different empirical correlations with shear wave velocity V_s and horizontal stress index K_D. Analytical data confirmed the observed occurrence of the liquefaction in Vittorito, even if the acceleration field in the area, produced by the L’Aquila earthquake, was very low.