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1.
The coda wave amplitude is used to calibrate the moment–magnitude scale of the Vrancea (Romania) intermediate depth earthquakes. The proportionality between seismic moment and coda wave amplitude is supposed to infer a relation connecting the magnitude, the coda amplitude and the corresponding time in coda (measured from the origin time). The data set consists of waveforms recorded by the Romanian telemetered network at several seismic stations, such as Muntele Rou (MLR), Vrâncioaia (VRI), Carcaliu (CFR) and Topalu (TLB). Our results are in good agreement with the moment–magnitude scale for Vrancea subcrustal events. The independence of the two approaches allows for the verification of the local magnitude scale for the Vrancea subcrustal earthquakes. Average relations among coda amplitude, magnitude ML and coda duration are obtained for the above-mentioned stations. 相似文献
2.
The possibility that the Earth's tides are a triggering factor of Vrancea subcrustal earthquakes is investigated in the first part of this paper. A possible correlation between Vrancea subcrustal earthquakes and geomagnetic jerks is demonstrated in the second part. The last part of the paper presents a number of results concerning a possible relationship between the regularities of strong Vrancea subcrustal seismicity and the Chandler nutation parameters. An attempt is made to integrate all of these phenomena in a more general framework that takes into account physical processes in the Earth mantle and core. A long-term prediction of the next strong Vrancea earthquake is finally attempted. 相似文献
3.
A. J. Haines 《Tectonophysics》1983,93(3-4)
Before the introduction in 1977 of new procedures for calculating the local magnitudes of New Zealand earthquakes, these were calculated using a derivative of Richter's method for Southern California. There are systematic differences between the magnitudes calculated by the two methods which are functions of position, magnitude and the types of seismometer recording the event. Usually the difference is small, though, for large earthquakes in particular, it can be close to unity.Differences of order unity are often observed between mB values reported by the ISC and both sets of local magnitudes. There appears to be no relationship between the local magnitudes, which now allow for the nature of wave propagation below New Zealand, and those reported by the ISC. 相似文献
4.
S. L. Soloviev 《Natural Hazards》1990,3(2):183-202
A list of 300 tsunamis and similar phenomena known in the Mediterranean is given. Data reliability and wave intensity are estimated; mechanisms of tsunami generation are indicated and data from literature sources on the coordinates and magnitudes of tsunamigenic earthquakes are cited. Eighteen zones of excitation and manifestation of tsunamis are identified which can be integrated into four groups with respect to the recurrence period and maximum intensity of the tsunamis. The strongest tsunamis are excited in the Aegean Sea, and the Hellenic and Calabrian island arcs. The focal depth of the earthquake-generating tsunamis in the Mediterranean is, on average, less than that in the Pacific. Correspondingly, the magnitude of tsunamigenic earthquakes is lower. According to preliminary estimates, the Mediterranean tsunamis attenuate with distance more rapidly than do those in the Pacific Ocean. 相似文献
5.
The city of Rome is subjected to moderate seismic risk due to both local and external seismicity. Up to now, the maximum intensity felt has never exceeded VIII MCS. The 1 November 1895 (I
o = VII) and 31 August 1909 (I
o = VI) earthquakes demonstrate that small local events can also cause damage in a large old city. In the present work, we have re-evaluated the intensity values of those two events by means of automatic processing. A comparison between the present results with geological evidence and previous studies is shown, especially for the historical centre of Rome. For the first time, the 1909 earthquake instrumental magnitudeM
L = 3.6 has been calculated from original recordings. 相似文献
6.
The Kamchatka peninsula, located in the far east of Russia, is a geologically active margin where the Pacific plate subducts beneath the North American and Eurasia plates. This area is characterised by frequent and strong seismic activity (magnitudes up to 8.5) and epicentres are generally distributed offshore along the eastern coast of the peninsula. For many years, hydrogeochemicals have been collected with a mean sampling frequency of three days in the form of the flow rate and the most common ions and gases in the groundwater of three deep wells in the southern area of the Kamchatka peninsula, where the capital city Petropavlovsk is located. Beginning in 1988, five earthquakes with M > 6.5 occurred in this area. These earthquakes were powerful enough to be considered as potential precursor sources in the sense that the stresses and strains building up before them might be expected to cause precursory activity. In order to reveal any possible precursors of these earthquakes, we analysed the hydrogeochemical data collected. We considered any signal having an amplitude three times the standard deviation to be an irregularity and we defined as an anomaly the existence of an irregularity occurring simultaneously in more than one parameter at each well. Then, on the basis of the worldwide past results and the time recurrence of the quoted earthquakes, we chose 158 days as the maximum temporal window between a possible anomaly and the subsequent earthquake. We identified some premonitory anomalies in hydrogeochemical parameters at different wells. On the basis of these results some earthquake forecasting criteria in southern Kamchatka may be tentatively formulated 相似文献
7.
lvaro Corral 《Tectonophysics》2006,424(3-4):177
The fulfillment of a scaling law for earthquake recurrence–time distributions is a clear indication of the importance of correlations in the structure of seismicity. In order to characterize these correlations we measure conditional recurrence–time and magnitude distributions for worldwide seismicity as well as for Southern California during stationary periods. Disregarding the spatial structure, we conclude that the relevant correlations in seismicity are those of the recurrence time with previous recurrence times and magnitudes; in the latter case, the conditional distribution verifies a scaling relation depending on the difference between the magnitudes of the two events defining the recurrence time. In contrast, with our present resolution, magnitude seems to be independent on the history contained in the seismic catalogs (except perhaps for Southern California for very short time scales, less than about 30 min for the magnitude ranges analyzed). 相似文献
8.
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 Mw 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. 相似文献
9.
Only few (six) focal mechanism, in CMT Catalog, have been so far known for intraplate shallow events in the Andean chain close to Chile–Argentina state border at latitudes ∼35° S. We add two more mechanisms, depths and moment magnitudes by carefully analyzing full waveforms of weak events recorded by broad-band stations of the Chile Argentina Geophysical Experiment (southern profile). The moment magnitudes of both events (Mw = 3.6 and 3.7) are lower than the duration magnitudes (Md = 4.0 and 4.29) reported by NEIC. The source depth, constrained by waveforms for one of the studied events (5.5–8.5 km) seems to be considerably shallower than the hypocenter depth located by means of arrival times (∼20 km). The waveform analysis was complemented by first-motion polarities which resulted in an uncertainty assessment of the focal mechanism. Event 1 (2001-11-03) has a strike-slip mechanism with a small normal component and almost vertical nodal planes in the north-south and east-west directions. The north-south nodal plane could be related to the Calabozos faults system. Event 2 (2002-02-16) has a strike-slip mechanism with a small thrust component. The latter event (its subhorizontal nodal plane) could be associated with the El Diablo-El Fierro fault system. Dextral strike-slip solutions are consistent with recent studies in the area. 相似文献
10.
In this work, Båth’s Law, the b-value in Gutenberg–Richter Law (G–R Law) in the form of the 1/β relationship, and both the a- and b-values in the G–R Law were introduced in order to estimate maximum aftershock magnitudes of earthquake sequences in the Taiwan region. The averaged difference of magnitude between the mainshock and the maximum aftershock is 1.20, and is consistent with Båth’s Law, however, with a large uncertainty. The large uncertainty implies that the difference may result from a variable controlled by other factors, such as the aftershocks number of an earthquake sequence and magnitude threshold for mainshock. With 1/β, since 86% of the earthquake sequences with a M ⩾ 6.0 mainshock follow this relationship, the upper bound of the maximum magnitude can be estimated for an earthquake sequence with a large mainshock. The a- and b-values in the G–R Law was also considered by evaluating maximum aftershock magnitudes. As there are low residuals between the model and the observations, the results suggest that the G–R Law is a good index for maximum aftershock magnitude determinations. In order to evaluate the temporal decays of maximum aftershock magnitudes, modified Omori’s Law was introduced. Using the approaches mentioned above, the maximum magnitudes and the temporal evolution of an earthquake sequence could be modeled. Among them, the model of the G–R Law has the best fit with observations for most of earthquake sequences. It shows its feasibility. The results of this work may benefit seismic hazards mitigation in the form of rapid re-evaluations for short-term seismic hazards immediately following devastating earthquakes. 相似文献
11.
松辽盆地裂谷期前火山岩与裂谷盆地关系及动力学过程 总被引：11，自引：0，他引：11
松辽盆地存在裂谷期前火山岩,之后上地壳脆性伸展发育半地堑裂谷盆地。裂谷期前火山岩近水平展布于基底之上,裂谷期,沉则分布于半地暂内,两者属于不同构造层。 相似文献
12.
Based on the improved hydrofracturing method, the in-situ principal stresses are determined in the north, northeast, south and the northwest of China, and the results of many fault-plane solutions, crustal deformations, geological and geophysical observations are used to discuss the distribution of subcrustal stress in space, the difference between seismically active regions and stable regions, and the variations of the stress field near the source region before and after the Tangshan earthquake. Finally, the characteristics of intraplate tectonic stress fields in China are explained in relation with the combined actions of the movement of the major Indian Ocean, Pacific and Philippine Sea plates. 相似文献
13.
The current geodynamics and tectonophysics of the Baikal rift system (BRS) as recorded in lithospheric stress and strain are discussed in the context of self organization of nonlinear dissipative dynamic systems and nonlinear media. The regional strain field inferred from instrumental seismic moment and fault radius data for almost 70,000 MLH ⩾ 2.0 events of 1968 through 1994 shows a complex pattern with zones of high strain anisotropy in the central part and both flanks of the rift system (the South Baikal, Hovsgöl, and Muya rift basins, respectively). The three zones of local strain anisotropy highs coincide with domains of predominantly vertical stress where earthquakes of different magnitudes are mostly of normal slip geometry. Pulse-like reversals of principal stresses in the high-strain domains appear to be nonlinear responses of the system to subcrustal processes. In this respect, the BRS lithosphere is interpreted in terms of the self organization theory as a geological dissipative system. Correspondingly, the domains of high strain anisotropy and stress change, called rifting attractor structures (RAS), are the driving forces of its evolution. The location and nonlinear dynamics of the rifting attractors have controlled lithospheric stress and strain of the rift system over the period of observations, and the same scenario may have been valid also in the Mesozoic-Cenozoic rifting history. The suggested model of a positive-feedback (fire-like) evolution of nonlinear dynamical systems with rifting attractors opens a new perspective on the current geodynamics and tectonophysics of the Baikal rift system. 相似文献
14.
Triassic strata of the Dockum Group in Texas comprise two major upward-fining alluvial-lacustrine depositional sequences.
The two sequences are represented by the (1) Santa Rosa-Tecovas, and (2) Trujillo-Cooper Canyon Formations. The second sequence
is much thicker than the first, and occupies a greater geographic part of the Dockum basin. Each sequence of alluvial and
lacustrine sediment accumulation is characterized by sediment derivation from a different source terrain. The unconformable
relationship between the two depositional sequences, the change in mineralogical composition and presumed source areas between
these units, differences in paleocurrent orientation between units, and evidence for intervening episodes of local deformation
indicate that the sequences are of tectonic origin. These strata are not the product of a single sediment dispersal system,
such as the centripetally-drained lacustrine delta complex previously envisioned for the Dockum basin. Both Dockum sequences
are comprised largely of two typical alluvial facies associations; stream channel facies, and overbank flood-plain facies,
that are similar to those described in nearly all fluvial deposits. In addition, the Dockum Group contains a peculiar lacustrine
facies that accumulated in local flood-plain depressions, and probably resulted from subsidence over areas of subsurface salt
dissolution. Vertebrate fossil assemblages are found in all three Dockum facies associations. Five fossiliferous sites in
the Dockum are discussed in the context of these three depositional settings. The Dockum tetrapod diversity is reviewed in
a hierarchical phylogeny with remarks on the history of collection, stratigraphic distribution of genera, and their taxonomic
status. The stratigraphic ranges of tetrapod taxa do not support the recently proposed successive Otischalkian, Adamanian,
Revueltian, and Apachean biochrons within the Dockum Group. Instead, a few index fossils provide a broad framework for correlation
of Late Triassic nonmarine strata of the Dockum with the Carnian and Norian Alpine marine stages. 相似文献
15.
本文通过对福建及其邻近地区五百多年来中强地震序列的研究,结果表明,该地区地震活动存在着明显的节律性,具有在节点上震级最大的特征,从而可预测该区下一次可能发生的中强地震的震级范围。 相似文献
16.
Subcrustal density inhomogeneities of Northern Eurasia as derived from the gravity data and isostatic models of the lithosphere 总被引：1，自引：0，他引：1
M. E. Artemjev M. K. Kaban V. A. Kucherinenko G. V. Demyanov V. A. Taranov 《Tectonophysics》1994,240(1-4):249-253
For the territory of Northern Eurasia (6°E–165°W; 30–75°N) the distribution of anomalous masses in the lithosphere has been estimated in accordance with the lithosphere isostatic model. The method of model construction is based on the admittance technique. The experimental admittance presents a relation between the part of the outer load uncompensated by the Moho undulations and the residual gravity field and is used to select the best model. The 1 × 1° averaged values of topography elevations, basement and Moho depths, sedimentary cover density and gravity anomalies have been used as initial data. According to the correlation equation relating the outer load and Moho depths, the mean density contrast between the lower crust and the subcrustal lithosphere is 0.43 g/cm3, but the Moho undulation can not provide complete isostatic equilibrium. In some areas, the part of the outer load uncompensated by Moho undulations may be as large as 107 kg/m2 and the residual gravity field is as intensive as + 260 mGal. Assuming that for loads of wavelength > 200 km, local isostatic compensation is valid, in accordance with the admittance analysis, the anomalous masses compensating for the part of the outer load, which is not compensated by Moho undulations, have to be located partly in the lower crust and in the subcrustal layer. The regional trend of anomalous compensating masses is negative under Western Europe, the Mediterranean, Eastern Asia and adjacent marginal seas, and positive under the East European Platform and Western and Central Asia. The local compensating masses correspond to particular tectonic units. The isostatic gravity anomalies of Northern Eurasia have been determined and the long-wave component of the field reflecting anomalous masses under the isostatic compensation level has been evaluated. 相似文献
17.
In this paper, we present three diverse types of applications of extreme value statistics in geology, namely: earthquakes magnitudes, diamond values, and impact crater size distribution on terrestrial planets. Each of these applications has a different perspective toward tail modeling, yet many of these phenomena exhibit heavy or long tails which can be modeled by power laws. It is shown that the estimation of important tail characteristics, such as the extreme value index, is directly linked to the interpretation of the underlying geological process. Only the most extreme data are useful for studying such phenomena, so thresholds must be selected above which the data become power laws. In the case of earthquake magnitudes, we investigate the use of extreme value statistics in predicting large events on the global scale and for shallow intracontinental earthquakes in Asia. Large differences are found between estimates obtained from extreme value statistics and the usually applied standard statistical techniques. In the case of diamond deposits, we investigate the impact of the most precious stones in the global valuation of primary deposits. It is shown that in the case of Pareto-type behavior, the expected value of few extreme stones in the entire deposit has considerable influence on the global valuation. In the case of impact crater distributions, we study the difference between craters distributions on Earth and Mars and distributions occurring on other planets or satellites within the solar system. A striking result is that all planets display the same distributional tail except for Earth and Mars. In a concluding account, we demonstrate the apparent loghyperbolic variation in all of the above-mentioned examples. 相似文献
18.
秦岭造山带主要构造岩石地层单元的构造性质及其大地构造意义 总被引：123，自引：18，他引：123
秦岭造山带由三大套构造岩石地层单位所构成，即１、二类不同的前寒武纪基底岩系；２、晚元古代－中三叠世主造山时期受板块构造和垂向增生构造控制的相关构造岩石地层单元；３、中新生代后造山期的陆内断陷与前陆和后陆盆地沉积及广泛的花岗岩浆活动。它们反映着秦岭带三个主要演化时期，在不同构造体制下的三种不同的基本地壳物质组成与结构。它们记录着秦岭造山带长期发展历史中的不同演化阶段的多种造山作用及其不同动力学机制的丰富信息。 相似文献
19.
《Earth》2008,88(3-4):94-112
It is generally found that the relative frequencies of occurrence of earthquakes of different magnitudes in seismogenic zones have a power law distribution. For a long-term dataset, the overall slope of this logarithmically transformed distribution is usually indicated by a best-fit straight line and expressed as a b-value. This slope is stable and normally lies between 0.8 and 1.2, the actual value depending on the region examined, and the threshold selected for data completeness. The linearity of the distribution can be used to make statistical inferences about the potential for larger events over the long run, and with appropriate reservations, may even be extrapolated to magnitudes that are beyond recent experience. We suggest the same information can also be viewed over shorter intervals in terms of an empirical piecewise distribution, with relative frequencies of occurrence at adjacent magnitude steps controlling the local slope of the distribution. An emergence, through time, of an excess number of lower magnitude earthquakes causes temporal changes to appear in the low-end piecewise gradients of this distribution. A marked excursion away from an overall uniform trend for the particular zone may be indicative of an imminent, larger event. On two separate occasions, in 1982 and 1997, such temporal variations were seen in the magnitude distributions of sequences of events near Tobago, West Indies, and used to anticipate subsequent damaging mainshocks. The recognition of temporal departures from overall linearity of the magnitude–frequency relation, in a suitable dataset, may thus provide an evidential element that can contribute to earthquake forecasting. This phenomenological approach was used in the analysis of the NEIC global dataset of earthquakes of magnitude 6.1 and bigger, for the period 1973–2003, to explore its wider applicability. Trends in the piecewise gradients of the global data were interpreted as pointing to an imminent great earthquake, perhaps exceeding magnitude 8.5; such an event did occur shortly afterwards in the form of the great Sumatran earthquake of 2004/12/26. Following that event, global magnitude production continued to exhibit sharp imbalances in the lower magnitude bins, indicating that another similar event was likely. The second Sumatran earthquake on 2005/03/28 satisfied that projection. Since that time, a magnitude production imbalance persists in the global dataset suggesting the system could be poised to output an earthquake (or earthquakes) in the magnitude range 8.6–9.0 or even greater. This contribution describes the piecewise gradient approach and examines its application to global earthquake data. 相似文献
20.
SUMMARY
A comparison is made between the void ratio and pressure relationships resulting from a laboratory consolidation test and a sedimentation-compression computation on a short core of calcareous mud or ooze of low plasticity. Geo-technical measurements of grain size, bulk density, Atterberg limits, water content, vane shear strength, pore-water salinity, and carbonate content are graphically related to depth in the core. Results of the laboratory consolidation test on this material differ markedly from the in-place relationship between void ratio, or water content, and the effective overburden pressure, or burial depth, shown by the sedimentation-compression curve. The previous maximum consolidation pressure, based on laboratory consolidation test data, is about 60 times greater than the computed in-place effective overburden pressure. An explanation for this difference would include the different magnitudes of time available for consolidation, cementation occurring in-place, and orientation of the constituents. It is suggested that results of the consolidation test on carbonate muds or oozes should be interpreted with caution for geological and engineering purposes. 相似文献
A comparison is made between the void ratio and pressure relationships resulting from a laboratory consolidation test and a sedimentation-compression computation on a short core of calcareous mud or ooze of low plasticity. Geo-technical measurements of grain size, bulk density, Atterberg limits, water content, vane shear strength, pore-water salinity, and carbonate content are graphically related to depth in the core. Results of the laboratory consolidation test on this material differ markedly from the in-place relationship between void ratio, or water content, and the effective overburden pressure, or burial depth, shown by the sedimentation-compression curve. The previous maximum consolidation pressure, based on laboratory consolidation test data, is about 60 times greater than the computed in-place effective overburden pressure. An explanation for this difference would include the different magnitudes of time available for consolidation, cementation occurring in-place, and orientation of the constituents. It is suggested that results of the consolidation test on carbonate muds or oozes should be interpreted with caution for geological and engineering purposes. 相似文献