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1.
A moderate-sized (Mw 5.3) earthquake occurred in the Dead Sea basin on February 11, 2004. A rigorous seismological analysis of the main shock and numerous aftershocks suggests that seismogenic structure was a secondary, antithetic fault within the Dead Sea fault system. The main shock is well located using all available regional seismic stations, and 43 aftershocks were precisely located relative to the main shock using a double difference algorithm. The first motion, focal mechanism for this earthquake demonstrates NNW–SSE and ENE–WSW striking nodal planes, and the aftershocks distribution is consistent with the latter — indicating a right-lateral sense of displacement. This orientation and sense of shear are consistent with similarly oriented geological faults around the Dead Sea basin — these structures are likely antithetic faults within the transform system. Although moderate in size, earthquakes that occur very close to the large Dead Sea fault system warrant consideration in the earthquake hazard assessment of the region: For example, owing to the proximity to the main fault, moderate earthquakes such as this may produce static changes in Coulomb stress along the main fault. 相似文献
2.
Effect of Aftershocks on Earthquake Hazard Estimation: An Example from the North Anatolian Fault Zone 总被引:2,自引:0,他引:2
In order to investigate the effect of aftershocks on earthquake hazard estimation, earthquake hazard parameters (m, b and Mmax) have been estimated by the maximum likelihood method from the main shocks catalogue and the raw earthquakes catalogue for the North Anatolian Fault Zone (NAFZ). The main shocks catalogue has been compiled from the raw earthquake catalogue by eliminating the aftershocks using the window method. The raw earthquake catalogue consisted of instrumentally detected earthquakes between 1900 and 1992, and historical earthquakes that occurred between 1000–1900. For the events of the mainshock catalogue the Poisson process is valid and for the raw earthquake catalogue it does not fit. The paper demonstrates differences in the hazard outputs if on one hand the main catalogues and on the other hand the raw catalogue is used. The maximum likelihood method which allows the use of the mixed earthquake catalogue containing incomplete (historical) and complete (instrumental) earthquake data is used to determine the earthquake hazard parameters. The maximum regional magnitude (Mmax, the seismic activity rate (m), the mean return period (R) and the b value of the magnitude-frequency relation have been estimated for the 24°–31° E, 31°–41° E, 41°–45° E sections of the North Anatolian Fault Zone from the raw earthquake catalogue and the main shocks catalogue. Our results indicate that inclusion of aftershocks changes the b value and the seismic activity rate m depending on the proportion of aftershocks in a region while it does not significantly effect the value of the maximum regional magnitude since it is related to the maximum observed magnitude. These changes in the earthquake hazard parameters caused the return periods to be over- and underestimated for smaller and larger events, respectively. 相似文献
3.
《Tectonophysics》1987,138(1):25-32
An earthquake (M = 5.9) occurred on November 7, 1983 in the Heze area, Shandong Province (35°17′ N, 115°17∃, H = 12 km). This earthquake belongs to the isolated type of earthquakes. There were no foreshocks; the aftershocks were few in number with their energy decreasing quickly.Within the area surrounding the main shock and up to about 200 km from the epicenter, several types of short-term and imminent anomalies were observed. The major characteristics of the anomalies are as follows:The short-term and imminent anomalies are relatively few in number. The maximum radius of the area where the anomalies occur is about 150–200 km from the epicenter. The time durations of what have been called short-term and imminent anomalies here are small, being
- 1.(1) from 10–20 days to 3–4 months and
- 2.(2) from 1–2 hours to 2–3 days, respectively. The premonitory information was scanty.
4.
M. D. Sharma 《Journal of Earth System Science》1997,106(1-2):15-26
Wave number discretization method is applied to study the near-field of seismic sources embedded in a cracked elastic solid. Near-field solutions are obtained for horizontal and vertical line forces. Effects of modifications in cracks of focal region on ground motion, in the near-field, are studied numerically for different ? values of crack density ? saturation of cracks ? width of cracks, and ? regimes of connection between cracks. An earthquake process is assumed to be going through five major stages. These stages represent continuous accumulation of stress, interconnections between cracks leading to eventual failure and drainage of fluid from cracks after the major shock. Variations in the velocity ratio of waves noted from accelerograms verify the process of preparation of an earthquake.P wave contribution to vertical acceleration is negligible when the source is a vertical line force andS wave contributes only a little to horizontal acceleration when the source is a horizontal line force. 相似文献
5.
The M w 7.8 2015 Gorkha earthquake and its aftershocks significantly impacted the lives and economy of Nepal. The consequences of landslides included fatalities, property losses, blockades of river flow, and damage to infrastructural systems. Co-seismic landslides triggered by this earthquake were significantly widespread and pose a major geodisaster. There were tens of thousands of landslides triggered by the earthquake, majority of which were distributed in between the epicenter of the main shock and the M w 7.3 aftershock. Although 14,670 landslides triggered by this earthquake were identified, only approximately 23% of them were of moderate to large scale with areas greater than 100 m2. Of the moderate- to large-scale landslides identified, just over 90% were triggered by the main shock and smaller aftershocks prior to the major (M w 7.3) aftershock, while nearly 10% were triggered by the ground shaking induced by the major aftershock. Moreover, the number of landslides triggered by the 2015 Gorkha earthquake, specifically by the main shock, was slightly more than the expected number of landslides for the recorded maximum peak ground acceleration (PGA) in comparison to the co-seismic landslides triggered by 26 earthquakes. Over 90% of those moderate- to large-scale landslides were concentrated within the estimated fault rupture surface. Majority of these moderate- to large-scale landslides were disrupted failures with over 96% of which were classified as earth falls. However, the majority of small-scale landslides were rock or boulder falls. The most number of moderate- to large-scale landslides were triggered in the slate, shale, siltstone, phyllite, and schist of the Lesser Himalayan formation followed by an equally significant number in both schist, gneiss, etc. of the Higher Himalayan formation and the phyllite, metasandstone, schist, etc. of the Lesser Himalayan formation. The sizes (i.e., areas) of the landslides were lognormally distributed, with a mode area of 322.0 m2. Slope inclinations of the moderate- to large-scale landslides followed a normal distribution with a mean slope inclination of 32.6° and standard deviation of 13.5°. There exists a strong correlation between the number of landslides and the peak ground acceleration within the study area, specific for different geological formations. 相似文献
6.
In this study, stochastic finite fault modeling is used to simulate Uttarkashi (1991) and Chamoli (1999) earthquakes using all available source, path, and site parameters available for the region. These two moderate earthquakes are recorded at number of stations of a strong motion network. The predicted peak ground accelerations at these stations are compared with the observed data and the ground motion parameters are constrained. The stress drop of Uttarkashi and Chamoli earthquakes is constrained at 77 and 65?bars, respectively, whereas the quality factor Q C is 112 $ f^{0.97} $ and 149 $ f^{0.95} $ for these two regions. The high-frequency attenuation parameter Kappa is in the range 0.04?C0.05. The constrained ground motion parameters are then used to simulate Mw 8.5 earthquake in central seismic gap region of Himalaya. Two scenarios are considered with epicenter of future great earthquake at locations of Uttarkashi and Chamoli earthquakes using above constrained parameters. The most vulnerable towns are the towns of Dehradun and Almora where expected PGA is in excess of 600?cm/s2 at VS30 520?m/s when the epicenter of the great earthquake is at the location of Uttarkashi (1991) earthquake. The towns of Shimla and Chandigarh can expect PGA close to 200?cm/s2. Whereas when the epicenter of the great earthquake is at the location of Chamoli (1999) earthquake, the towns of Dehradun and Almora can expect PGA of around 500 and 400?cm/s2, respectively, at VS30 620?m/s. The National Capital Region, Delhi can expect accelerations of around 80?cm/s2 in both the cases. The PGA contour maps obtained in this study can be used to assess the seismic hazard of the region and identify vulnerable areas in and around central Himalaya from a future great earthquake. 相似文献
7.
8.
Laihunite Research Group 《中国地球化学学报》1982,1(1):105-114
Laihuite reported in the present paper is a new iron silicate mineral found in China with the following characteristics:
- This mineral occurs in a metamorphic iron deposit, associated with fayalite, hypersthene, quartz, magnetitc, etc.
- The mineral is opaque, black in colour, thickly tabular in shape with luster metallic to sub-metallic, two perfect cleavages and specific gravity of 3.92.
- Its main chemical components are Fe and Si with Fe3+>Fe2+. The analysis gave the formula of Fe Fe 1.00 3+ ·Fe 0.58 2+ ·Mg 0.03 2+ ·Si0.96O4.
- Its DTA curve shows an exothermic peak at 713°C.
- The mineral has its own infrared spectrum distinctive from that of other minerals.
- This mineral is of orthorhombic system; space group:C 2h /5 ?P21/c; unit cell:α=5.813ű0.005,b=4.812ű0.005,c=10.211ű0.005,β=90.87°.
- The Mössbauer spectrum of this mineral is given, too.
9.
《Tectonophysics》1987,138(1):79-92
Analysis of the space-time patterns of seismicity in the Himalaya plate boundary has established the existence of three seismic gaps:
- 1.(1) The “Kashmir gap” lying west of the 1905 Kangra earthquake;
- 2.(2) the “Central gap”, situated between the 1905 Kangra and the 1934 Bihar earthquakes;
- 3.(3) the “Assam gap” between the 1897 and 1950 Assam earthquakes.
10.
We analyze previously published geodetic data and intensity values for the M s = 8.1 Shillong (1897), M s = 7.8 Kangra (1905), and M s = 8.2 Nepal/Bihar (1934) earthquakes to investigate the rupture zones of these earthquakes as well as the amplification of ground motions throughout the Punjab, Ganges and Brahmaputra valleys. For each earthquake we subtract the observed MSK intensities from a synthetic intensity derived from an inferred planar rupture model of the earthquake, combined with an attenuation function derived from instrumentally recorded earthquakes. The resulting residuals are contoured to identify regions of anomalous intensity caused primarily by local site effects. Observations indicative of liquefaction are treated separately from other indications of shaking severity lest they inflate inferred residual shaking estimates. Despite this precaution we find that intensites are 1–3 units higher near the major rivers, as well as at the edges of the Ganges basin. We find evidence for a post-critical Moho reflection from the 1897 and 1905 earthquakes that raises intensities 1–2 units at distances of the order of 150 km from the rupture zone, and we find that the 1905 earthquake triggered a substantial subsequent earthquake at Dehra Dun, at a distance of approximately 150 km. Four or more M = 8 earthquakes are apparently overdue in the region based on seismic moment summation in the past 500 years. Results from the current study permit anticipated intensities in these future earthquakes to be refined to incorporate site effects derived from dense macroseismic data. 相似文献
11.
《Tectonophysics》1987,138(1):45-53
In this paper, the seismic pattern in Northern China from 30 ° to 42 ° N latitude and 104 ° to 125 ° E longitude, and the characteristics of the epicentral distribution before large events are presented. The results suggest that:
- 1.(1) the earthquakes in the region are mainly located in the orthogonal curvilinear network formed by the seismic belts;
- 2.(2) the larger earthquakes (M ⩾6) occurred mainly in the nodal regions of this grid:
- 3.(3) the strike of the fracture planes of the earthquakes coincided with the directions of the seismic belts;
- 4.(4) the pattern of medium strong earthquakes (M ⩾ 4.7) prior to thirteen large earthquakes (M⩾ 7) are analysed to be of three types:
- 4.1.(a) mainly arranged along the two intersecting belts,
- 4.2.(b) randomly distributed,
- 4.3.(3) forming seismic gaps.
12.
Mohammad Reza Mansouri Daneshvar Mahmood Khosravi Taghi Tavousi 《Natural Hazards》2014,74(3):1539-1553
Several studies have reported the increased values of surface-latent heat flux (SLHF) and rainfall events prior to the earthquakes as the seismic precursors. In order to investigate the variation of two mentioned atmospheric variables, we analyzed 39 major earthquakes in the Middle East based on the time series of NASA remote sensing data. On this basis, we observed that accumulated rainfall and SLHF of about 29 earthquakes were higher than 10 mm and 50 W/m2, respectively (~75 %), over 3–23 days prior to the main shock of major earthquakes. We believed that the records of atmospheric variables are the consequence of a seismic-triggered chain including of air ionization, surface-latent heat exhalation, water vapor condensation and subordinate rainfall as the atmospheric responses to lithospheric motions. This seismic triggering in the Middle East has averagely caused to accumulated rainfall of ~35 mm and maximum SLHF of ~115 W/m2 over the 3–23 days prior to 39 major earthquakes. To investigate of spatial correlation between earthquakes and atmospheric variations, we clustered 39 major earthquakes in eight seismological regions. Then, we estimated the moderate and strong correlation (R 2) between preceding times of earthquakes with magnitude of major earthquakes and their hypocenter depth equal to 0.48 and 0.68, respectively. 相似文献
13.
Dr. Wolfgang E. Krumbein 《International Journal of Earth Sciences》1971,60(2):438-471
The influence of bacteria on recent sediments was first discussed in 1885, whenFischer andGazert were discussing the cycle of substances in the sea as well as in sediments. The influence of bacteria on the cycling of C, N, S, P in recent sediments and the open sea was soon accepted by marine geologists. Nevertheless, only very few experiments have, so far, shown more than qualitative and quantitative data collection in various restricted areas. This is due to the extensive and complicated chain of reactions on the surface of sediments and in the sediment itself. Biologists are asking for the amount of organic and inorganic matter which is reworked and released to the sea. Geologists usually emphasize the amount of substances which are sedimentated. For biologists the sediment is only part of their dominant ecosystem (the sea). While, for geologists the “sea” is only furnishing and influencing their first range system sediment. How much then, are bacteria involved in the slow process of conversion from a recent sediment to sedimentary rocks? Bacteria influence more or less strongly and to a more or less advanced degree of diagenesis:
- The organic matter in sediments and the final form in which it is found.
- The anions CO3 2?, NO3 ?, OH-, SO4 2?, PO4 3? as well as their intermediate stages and the resulting minerals.
- The cations H+, NH4 +, Ca2+, Fe2+, Fe3+, and a series of metals which are dissolved or precipitated by microbial activities as for example Fe, Mn, Cu, Ag, V, Co, Mo, Ni, U, Se, Zn.
- The equilibrium of silicium. At least diatoms and radiolarians are precipitating silica, while other reactions which have been proved are not yet shown to influence marine sediments.
- pH-values and oxidation-reduction potentials of the sediment.
- The composition of interstitial waters.
- The surface activity of minerals, since bacteria are growing especially on particle surfaces.
- The energy content and temperature of sediments.
- The texture of fine grained sediments.
- The fossilization of microfauna, macrofauna and trace fossils.
14.
E. H. Brown 《Contributions to Mineralogy and Petrology》1977,64(2):123-136
Phase relations of pumpellyite, epidote, lawsonite, CaCO3, paragonite, actinolite, crossite and iron oxide are analysed on an Al-Ca-Fe3+ diagram in which all minerals are projected from quartz, albite or Jadeite, chlorite and fluid. Fe2+ and Mg are treated as a single component because variation in Fe2+/Mg has little effect on the stability of phases on the diagram. Comparison of assemblages in the Franciscan, Shuksan, Sanbagawa, New Caledonia, Southern Italian, and Otago metamorphic terranes reveals several reactions, useful for construction of a petrogenetic grid:
- lawsonite+crossite + paragonite = epidote+chlorite + albite + quartz + H2O
- lawsonite + crossite = pumpellyite + epidote + chlorite + albite+ quartz + H2O
- crossite + pumpellyite + quartz = epidote + actinolite + albite + chlorite + H2O
- crossite + epidote + quartz = actinolite + hematite + albite + chlorite + H2O
- calcite + epidote + chlorite + quartz = pumpellyite + actinolite + H2O + CO2
- pumpellyite + chlorite + quartz = epidote + actinolite + H2O
15.
The seismic anisotropy of the mantle is studied based on the data of S and ScS waves from earthquakes occurred in the mantle transition zone over the period of 2007–2013 and recorded by seismic stations in the continental margin of Asia, on Sakhalin Island, and in the southern part of the Kamchatka Peninsula. The measurements of the azimuths of polarization of the fast S and ScS waves in the continental margin of Asia show that they are predominantly oriented in the E–SE directions. Based on the distribution of the shear wave splitting parameters, the symmetry of the medium can be described in terms of a transversely isotropic model with a horizontal symmetry axis and may correspond to horizontal flow in the upper mantle beneath the Amur Plate. The fast azimuths of polarization of ScS wave, which were determined to be of N–NE directions in the northern area of Sakhalin Island and in the continental part of Asia, may correspond to an inclined flow under the conditions of oblique subduction and complex geometry of the downgoing Pacific Plate. In the south of the Kamchatka Peninsula, the S- and ScS-wave azimuths of polarization from the M 8.4 Sea of Okhotsk earthquake are determined to be oriented along the direction of the Pacific Plate motion. The fast-S-wave azimuths of polarization from the aftershocks of the Sea of Okhotsk earthquake and from other large events of 2008–2009 are determined to be nearly parallel to the motion trend of the Pacific Plate, but orthogonal to it for the events of 2008–2009. On the basis of the distribution of azimuths of polarization of the fast S waves, the symmetry of the medium can be described in terms of a transversely isotropic model with the symmetry axis inclined orthogonally to the plane of downgoing plate and oriented westward orthogonally to the trench strike. 相似文献
16.
S. Trupti K. Goverdhan K. N. S. S. S. Srinivas P. Prabhakar Prasad T. Seshunarayana 《Natural Hazards》2013,69(1):953-964
Site classification studies play a vital role in earthquake hazard assessment since in situ ground conditions substantially affect the characteristics of incoming seismic waves during earthquakes. Flat areas along the coast and rivers generally consist of thick layers of soft clay and sand. Such deposits amplify certain frequencies of ground motion, thereby attributing to an increase in the damage due to an earthquake. Hence, site classification studies have been carried out using shear-wave velocity, ground response, and corresponding amplification at 83 locations in Pondicherry, a coastal city in India. The present study is aimed at estimating the shear-wave velocity through multichannel analysis of surface waves and to compute the average shear-wave velocity (V S 30 ), stiffness, and N values using empirical relations. Further, site-response studies (horizontal-to-vertical spectral ratio) were conducted to estimate the ground-response frequencies and corresponding amplifications through Nakamura technique. From the results, the study area was classified into three types, i.e., C-class: with V S 30 in the range of 360–760 m/s, D-class: with V S 30 in the range of 180–360 m/s, and E-class: with V S 30 < 180 m/s following the National Earthquake Hazard Reduction Programme norms (BSSC in NEHRP recommended provisions for seismic regulations for new buildings and other structures (FEMA 450), part 1: provisions. Building Seismic Safety Council for the Federal Emergency Management Agency, Washington, 2003). Finally, a site classification map for Pondicherry region has been prepared, which can be used in urban planning and strengthening of existing structures against future earthquakes. 相似文献
17.
Thermodynamic computer modeling was carried out to evaluate the formation of the chemical composition of main geochemical types of groundwaters. An explanation was proposed for the geochemical evolution of underground saline waters and brines along the calcic and sodic trends, the inversion of groundwater in the deep horizons of sedimentation structures, and the geochemical diversity of CO2-rich waters in crystalline rocks. The occurrence of hydrogeochemical processes is controlled by the physicochemical conditions of the state of the water-rock-gas system. The following parameters (boundary conditions) are critical in natural hydrogeologic environments: the mass ratio of interacting rock and water (R/W), the openness (closeness) of hydrogeochemical systems with respect to CO2 and O2, the chemical and mineral composition of rocks, and temperature-pressure conditions. The estimation of boundary conditions showed the following.
- The petrochemical type of rock affects the composition of the aqueous phase through the dissolution rates of minerals, especially volatile-bearing ones. A decrease in water exchange and an increase in R/W (10?6??102) are accompanied by an increase in the salinity of the aqueous phase and an increase in the fraction of Cl, Na, and Ca (in a closed system) or HCO3, Cl, and Na (in a system open to CO2).
- The composition of the aqueous phase of water-rock systems is most strongly affected by the abundance in the rock of extractable Cl and reactive organic matter, which controls the geochemical type of the aqueous phase and its position in the Hardie-Eugster diagram.
- The composition of the aqueous phase is shifted into the calcic field of the Hardie-Eugster diagram at the closure of the water-rock system and into the carbonate field at the opening of the water-rock system to CO2. Waters showing pH ?? 8.5 are formed in feldspathic rocks with low contents of extractable volatiles. Alkaline waters with pH > 9 are formed in water-rock systems (a) under the influence of organic matter and (b) by the evaporative concentration waters under surface conditions.
- The higher the degree of seawater concentration and the lower the R/W value, the more significant the effect of seawater composition on the aqueous phase chemistry of the water-rock system. With increasing degree of seawater concentration, the composition of the aqueous phase changes in the sequence Cl-SO4-Na-Mg- ?? Cl-SO4-Mg-Na?? Cl-Mg (at low R/W) and Cl-Na ?? Cl-Na-Mg (at high R/W). The influence of the petrochemical type of rock and CO2 partial pressure, on the geochemical type of the aqueous phase in the seawater-rock system is more significant at high R/W.
- A temperature increase shifts the acid-base state of the aqueous phase into the alkaline region and its redox state into the reducing region.
18.
Scaling properties of earthquake populations bear the major information on the physics of the source process of an earthquake. To determine scaling properties, source spectra of more than 400 earthquakes of Kamchatka were determined in a frequency range 0.1–30 Hz using materials of digital registration of PET station, and characteristic frequencies of earthquakes were estimated. The range of magnitudes is 4–6.5, the range of distances is 80–220 km. To enable reduction of a spectrum to the source, attenuation properties of the medium around PET were determined beforehand. It is revealed that source spectra show several corner (characteristic) frequencies: f c1, f c2 and f c3; where the spectral trend changes: from f 0 to f ?1, from f ?1 to f ?2, and from f ?2 to f ?3, respectively. Although in some cases f c1 ≈ f c2 in agreement with the usual ω?2 spectral model, the main part of spectra has more complicated character. For a large part of the studied earthquakes a source-controlled upper cutoff of acceleration spectrum, or corner frequency f c3, is observed. This is an important fact, as the existence of f c3 (source-controlled f max) is not recognized in the bulk of the seismological literature. For f c1, the observed scaling agrees with the usual hypothesis of similarity of the earthquake sources of different size (magnitude); it is close to f c1 ~ M 0 ?1/3 , where M 0 is seismic moment. For f c2, scaling is close to f c2 ~ M 0 ?0.17 ~ f c1 0.5 , that indicates an expressed violation of similarity. For f c3, scaling is close to f c2 ~ M 0 ?0.08 ~ f c1 0.25 , so that similarity is broken even sharper in this case. Hypotheses about possible causes of the observed scaling are discussed. 相似文献
19.
20.
Dr. Barbara Theilen-Willige 《International Journal of Earth Sciences》1982,71(1):318-327
The following facts have supported the origin of the Araguainha circular structure in Central Brazil by a meteoritic impact:
- the almost circular contour
- the impact-morphologic sequence including a central uplift, ring walls and a basin rim of escarpments
- outcrops of suevites and mixed breccias
- the evidence of shock metamorphism
- the presence of shatter cones, and
- negative anomalies of the total intensity of the magnetic field at the center of the ring structure.