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1.
The paper describes a temporary seismic project aimed at developing the national database of natural seismic activity for seismic hazard assessment, officially called “Monitoring of Seismic Hazard of Territory of Poland” (MSHTP). Due to low seismicity of Poland, the project was focused on events of magnitude range 1–3 in selected regions in order to maximize the chance of recording any natural event. The project used mobile seismic stations and was divided into two stages.Five-year measurements brought over one hundred natural seismic events of magnitudes ML range 0.5–3.8. Most of them were located in the Podhale region in the Carpathians. Together with previously recorded events this made it possible to conduct a preliminary study on ground motion prediction equation for this region. Only one natural event, of magnitude ML = 3.8, was recorded outside the Carpathians in a surprising location in central-west Poland.  相似文献   

2.
— Seismic hazard analysis methods in mines are reviewed for the purpose of selecting the best technique. To achieve this goal, the most often-used hazard analysis procedure, which is based on the classical frequency-magnitude Gutenberg-Richter relation, as well as alternative procedures are investigated.¶Since the maximum regional seismic event magnitude m max is of paramount importance in seismic hazard analysis, this work provides a generic formula for the evaluation of this important parameter. The formula is capable of generating solutions in different forms, depending on the assumptions of the model of the magnitude distribution and/or the available information regarding past seismicity. It includes the cases (i) in which seismic event magnitudes are distributed according to the truncated frequency-magnitude Gutenberg-Richter relation, and (ii) in which no specific model of the magnitude distribution is assumed.¶Both synthetic, Monte-Carlo simulated seismic event catalogues, and actual data from the copper mine in Poland and gold mine in South Africa, are used to demonstrate the discussed hazard analysis techniques.¶Our studies show that the non-parametric technique, which is independent of the assumed model of the distribution of magnitude, provides an appropriate tool for seismic hazard assessment in mines where the magnitude distribution can be very complex.  相似文献   

3.
The refinement of the accuracy and resolution of the monthly global gravity field models from the GRACE satellite mission, together with the accumulation of more than a decade-long series of these models, enabled us to reveal the processes that occur in the regions of large (Mw≥8) earthquakes that have not been studied previously. The previous research into the time variations of the gravity field in the regions of the giant earthquakes, such as the seismic catastrophes in Sumatra (2004) and Chile (2010), and the Tohoku mega earthquake in Japan (2011), covered the coseismic gravity jump followed by the long postseismic changes reaching almost the same amplitude. The coseismic gravity jumps resulting from the lower-magnitude events are almost unnoticeable. However, we have established a long steady growth of gravity anomalies after a number of such earthquakes. For instance, in the regions of the subduction earthquakes, the growth of the positive gravity anomaly above the oceanic trench was revealed after two events with magnitudes Mw=8.5 in the Sumatra region (the Nias earthquake of March 2005 and the Bengkulu event of September 2007 near the southern termination of Sumatra Island), after the earthquake with Mw=8.5 on Hokkaido in September 2007, a doublet Simushir earthquake with the magnitudes Mw = 8.3 and 8.1 in the Kuriles in November 2006 and January 2007, and after the earthquake off the Samoa Island in September 2009 (Mw=8.1). The steady changes in the gravity field have also been recorded after the earthquake in the Sichuan region (May 2008, Mw = 8.0) and after the doublet event with magnitudes 8.6 and 8.2, which occurred in the Wharton Basin of the Indian Ocean on April 11, 2012. The detailed analysis of the growth of the positive anomaly in gravity after the Simushir earthquake of November 2006 is presented. The growth started a few months after the event synchronously with the seismic activation on the downdip extension of the coseismically ruptured fault plane zone. The data demonstrating the increasing depth of the aftershocks since March 2007 and the approximately simultaneous change in the direction and average velocity of the horizontal surface displacements at the sites of the regional GPS network indicate that this earthquake induced postseismic displacements in a huge area extending to depths below 100 km. The total displacement since the beginning of the growth of the gravity anomaly up to July 2012 is estimated at 3.0 m in the upper part of the plate’s contact and 1.5 m in the lower part up to a depth of 100 km. With allowance for the size of the region captured by the deformations, the released total energy is equivalent to the earthquake with the magnitude Mw = 8.5. In our opinion, the growth of the gravity anomaly in these regions indicates a large-scale aseismic creep over the areas much more extensive than the source zone of the earthquake. These processes have not been previously revealed by the ground-based techniques. Hence, the time series of the GRACE gravity models are an important source of the new data about the locations and evolution of the locked segments of the subduction zones and their seismic potential.  相似文献   

4.
The Comprehensive Nuclear-Test-Ban Treaty (CTBT), a global ban on nuclear explosions, is currently in a ratification phase. Under the CTBT, an International Monitoring System (IMS) of seismic, hydroacoustic, infrasonic and radionuclide sensors is operational, and the data from the IMS is analysed by the International Data Centre (IDC). The IDC provides CTBT signatories basic seismic event parameters and a screening analysis indicating whether an event exhibits explosion characteristics (for example, shallow depth). An important component of the screening analysis is a statistical test of the null hypothesis H 0: explosion characteristics using empirical measurements of seismic energy (magnitudes). The established magnitude used for event size is the body-wave magnitude (denoted m b) computed from the initial segment of a seismic waveform. IDC screening analysis is applied to events with m b greater than 3.5. The Rayleigh wave magnitude (denoted M S) is a measure of later arriving surface wave energy. Magnitudes are measurements of seismic energy that include adjustments (physical correction model) for path and distance effects between event and station. Relative to m b, earthquakes generally have a larger M S magnitude than explosions. This article proposes a hypothesis test (screening analysis) using M S and m b that expressly accounts for physical correction model inadequacy in the standard error of the test statistic. With this hypothesis test formulation, the 2009 Democratic Peoples Republic of Korea announced nuclear weapon test fails to reject the null hypothesis H 0: explosion characteristics.  相似文献   

5.
According to S.A. Fedotov’s long-term earthquake forecast, the Middle Kuril Is. has long (since 1965) been a likely location for the next M ≥ 7.7 earthquake, i.e., a seismic gap. The present study integrates seismological, geological, and geophysical data to assess the earthquake potential of the gap prior to November 15, 2006. Seismological data were used to carry out a comparative analysis of 3D seismic energy density for three zones of the Kuril region. The density for the Middle Kuril Is. turned out to be twice as small as that for the North Kuril Is. and nearly six times as small as that for the South Kurils. Various parameters of the seismic process for the Kuril region have been estimated in quantitative terms. It is shown that the rate of completely reported (M ≥ 6) earthquakes occurring down to 70 km depth in the Middle Kuril Is. is approximately three times as small as that for the entire Kuril arc. Increased heat flow was recorded there (up to 100 mW/m2). The top of the high conductivity layer is shallower (at a depth of 100 km). The trends of major faults and other seismotectonic features have been taken into account. Based on these data (prior to November 15, 2006), the previous conclusion about the low seismic activity of the Middle Kuril Is. was corroborated. Two great earthquakes occurred in the region on November 15, 2006 (M w = 8.3) and January 13, 2007 (M w = 8.1) with subsequent tsunami waves. The erroneous inference as to low seismic activity was related to the fact that the seismic cycle in the Middle Kuril Is. may be as long as 150–200 years. We come to the conclusion that an analysis of the level of seismic activity for the region should start with the construction of standardized recurrence curves and determining the magnitude of the maximum possible earthquake.  相似文献   

6.
Earthquake of November 30, 2004, in Podhale region, southern Poland, was of unexpectedly big size in this area of weak seismicity. As Poland is considered a country of low seismicity, the earthquake has caused concern about seismic hazard in Poland, especially since it took place shortly after the even more unexpected Kaliningrad Region, Russia, earthquakes of September 21, 2004, that inflicted minor damage in northern Poland. The paper presents the findings on the Podhale earthquake which reached macroseismic intensity up to 7 and magnitude 4.7 (m b ; ISC). The event was felt up to a distance of about 100 km and inflicted slight damage to buildings in its narrow epicentral area, thus evidencing its relatively shallow depth. The quake has been located near the village of Skrzypne, about 15 km west-southwest of the district capital Nowy Targ. The source mechanism has been found to be of dip slip normal fault type, although a problem remains of association of this mechanism with known tectonic dislocations in the region. The earthquake has been followed by a long series of aftershocks. Their distribution in time is also studied and the biggest aftershocks have been located.  相似文献   

7.
High energy release during seismic events induced by mining operation is one of the major dangers perturbing production in underground mines. In this work, temporal changes of seismic event parameters for one of the Rudna Mine (Poland) panels are investigated. The study aim was to find whether the temporal clustering of smaller events in different parameters can be observed before and after the high energy events (Ml?≥?3) in the mining panel. The method chosen for analysis was the study of temporal variation of fractal dimension of the seismic events parameter sets composed from: the interevent epicentral distance (dr), logarithm of seismic energy (lE), and interevent energy coefficient (dlE), which is the absolute difference between logarithms of energy of two consecutive events. Temporal variations study was performed in equivalent dimension (ED) space. The transformation of the seismic source parameters into ED space allowed to estimate and compare the temporal changes of the fractal dimension of different parameter spaces using the same method—correlation fractal dimension, and then easily compare the obtained temporal changes of fractal dimension of different parameter sets. The effect of grouping is expressed by decrease of fractal dimension, which is connected with the similarity of events parameter values. The temporal changes of the fractal dimension of seismicity before the strong induced events would indicate some initiation phase of the process leading to the high energy release. In the case of the studied Rudna Mine panel, the temporal behavior of the fractal dimension values in different parameter spaces before seismic events showed significant changes before three out of four events with CLVD dominant source mechanisms.  相似文献   

8.
On July 29, 2021, a large earthquake of MW8.2 occurred south of the Alaska Peninsula. To investigate the spatial-temporal changes of crustal stress in the earthquake-stricken area before this event, we selected 159 earthquakes of 4.7 ≤ MW ≤ 6.9 that occurred in the epicentral region and its surroundings between January 1980 and June 2021 to study the temporal variation and spatial distribution of their apparent stress. In addition, we analyzed the correlation between seismic activities and Earth’s rotation and explored the seismogenic process of this earthquake. The crustal stress rose from January 2008 to December 2016. This period was followed by a sub-instability stage from January 2017 until the occurrence of the MW8.2 earthquake. The average rate of apparent stress change in the first five years of the stress increase period was roughly 2.3 times that in the last four years. The lateral distribution of the apparent stress shows that the areas with apparent stress greater than 1.0 MPa exhibited an expanding trend during the seismogenic process. The maximum apparent stress was located at the earthquake epicenter during the last four years. The distribution of the apparent stress in the E-W vertical cross section revealed that an apparent stress gap formed around the hypocenter during the first five years of the stress increase period, surrounded by areas of relatively high apparent stress. After the Alaska earthquake, most parts of this gap were filled in by aftershocks. The seismic activities during the sub-instability stage exhibited a significant correlation with Earth’s rotation.  相似文献   

9.
《Geofísica Internacional》2013,52(2):173-196
An analysis of local and regional data produced by the shallow, thrust Ometepec-Pinotepa Nacional earthquake (Mw 7.5) of 20 March 2012 shows that it nucleated at 16.254°N 98.531°W, about 5 km offshore at a depth of about 20 km. During the first 4 seconds the slip was relatively small. It was followed by rupture of two patches with large slip, one updip of the hypocenter to the SE and the other downdip to the north. Total rupture area, estimated from inversion of near-source strong-motion recordings, is ~25 km × 60 km. The earthquake was followed by an exceptionally large number of aftershocks. The aftershock area overlaps with that of the 1982 doublet (Mw 7.0, 6.9). However, the seismic moment of the 2012 earthquake is ~3 times the sum of the moments of the doublet, indicating that the gross rupture characteristics of the two earthquake episodes differ. The small-slip area near the hypocenter and large-slip areas of the two patches are characterized by relatively small aftershock activity. A striking, intense, linear NE alignment of the aftershocks is clearly seen. The radiated energy to seismic moment ratios, (Es/M0), of five earthquakes in the region reveal that they are an order of magnitude smaller for near-trench earthquakes than those that occur further downdip (e.g., 2012 and the 1995 Copala earthquakes). The near-trench earthquakes are known to produce low Amax. The available information suggests that the plate interface in the region can be divided in three domains. (1) From the trench to a distance of about 35 km downdip. In this domain M~6 to 7 earthquakes with low values of (Es/M0) occur. These events generate large number of aftershocks. It is not known whether the remaining area on this part of the interface slips aseismically (stable sliding) or is partially locked. (2) From 35 to 100 km from the trench. This domain is seismically coupled where stick-slip sliding occurs, generating large earthquakes. Part of the area is probably conditionally stable. (3) From 100 to 200 km from the trench. In this domain slow slip events (SSE) and nonvolcanic tremors (NVT) have been reported.The earthquake caused severe damage in and near the towns of Ometepec and Pinotepa Nacional. The PGA exceeded 1 g at a soft site in the epicentral region. Observed PGAs on hard sites as a function of distance are in reasonable agreement with the expected ones from ground motion prediction equations derived using data from Mexican interplate earthquakes. The earthquake was strongly felt in Mexico City. PGA at CU, a hard site in the city, was 12 gal. Strong-motion recordings in the city since 1985 demonstrate that PGAs during the 2012 earthquake were not exceptional, and that similar motion occurs about once in three years.  相似文献   

10.
On October 27, 2004, a moderate size earthquake occurred in the Vrancea seismogenic region (Romania). The Vrancea seismic zone is an area of concentrated seismicity at intermediate depths beneath the bending area of the southeastern Carpathians. The 2004 M w?=?6 Vrancea subcrustal earthquake is the largest seismic event recorded in Romania since the 1990 earthquakes. With a maximum macroseismic intensity of VII Medvedev–Sponheuer–Kárník (MSK-64) scale, the seismic event was felt to a distance of 600 km from the epicentre. This earthquake caused no serious damage and human injuries. The main purpose of this paper is to present the macroseismic map of the earthquake based on the MSK-64 intensity scale. After the evaluation of the macroseismic effects of this earthquake, an intensity dataset has been obtained for 475 sites in the Romanian territory. Also, the maximum horizontal accelerations recorded in the area by the K2 network are compared to the intensity values.  相似文献   

11.
— An algorithm recently developed by RUNDLE et al. (2002) to find regions of anomalous seismic activity associated with large earthquakes identified the location of an M w = 5.6 earthquake near Calexico, Mexico. In this paper we analyze the regional seismicity before this event, and a nearby M w = 5.7 event, using time-to-failure algorithms developed by BOWMAN et al. (1998) and BOWMAN and KING (2001a,b). The former finds the radius of a circular region surrounding the epicenter that optimizes the time-to-failure acceleration of seismic release. The latter optimizes acceleration based on the expected stress accumulation pattern for a dislocation source. Both methods found a period of accelerating seismicity in an optimal region, the size of which agrees with previously proposed scaling relations. This positive result suggests that the Rundle algorithm may provide a useful technique to identify regions of accelerating seismicity, which can then be analyzed using signal optimization time-to-failure techniques.  相似文献   

12.
The paper discusses problems of seismic zoning of the Kaliningrad region, where a series of perceptible earthquakes occurred in 2004; the strongest event had a magnitude of M s = 4.3 and produced shakings of an intensity of 6 in the coastal zone of the Sambiiskii Peninsula, classified as a 5-intensity zone. The enhanced seismic effect is shown to be caused by bad ground conditions, long-term action of seismic effects, resonance phenomena, and other factors. To gain additional constraints on the seismic hazard degree in the Kaliningrad region, the paper discusses an improved version of the model of earthquake sources underlying the compilation of normative maps of seismic zoning (OSR-97). Modified fragments of OSR-97 probability maps of the Kaliningrad region are constructed at different levels of probability that the seismic effect indicated in the maps will be exceeded over 50 yr. It is shown that additional seismological investigations should be conducted in this region.  相似文献   

13.
This study analyses the temporal clustering, spatial clustering, and statistics of the 2012–2013 Torreperogil-Sabiote (southern Spain) seismic swarm. During the swarm, more than 2200 events were located, mostly at depths of 2–5 km, with magnitude event up to mbLg 3.9 (Mw 3.7). On the basis of daily activity rate, three main temporal phases are identified and analysed. The analysis combines different seismological relationships to improve our understanding of the physical processes related to the swarm's occurrence. Each temporal phase is characterized by its cumulative seismic moment. Using several different approaches, we estimate a catalog completeness magnitude of mc≅ 1.5. The maximum likelihood b-value estimates for each swarm phase are 1.11 ± 0.09, 1.04 ± 0.04, and 0.90 ± 0.04, respectively. To test the hypothesis that a b-value decrease is a precursor to a large event, we study temporal variations in b-value using overlapping moving windows. A relationship can be inferred between change in b-value and the regime style of the rupture. b-values are indicators of the stress regime, and influence the size of ruptures. The fractal dimension D2 is used to perform spatial analysis. Cumulative gamma and beta functions are used to analyse the behaviour of inter-event distances during the earthquake sequence.  相似文献   

14.
The Sakarya prefecture is an interesting area with various seismicity types. This activity comes from earthquakes occurring at the North Anatolian Fault Zone and from a few quarry blast areas in the region. These quarry blast recordings produce errors in the determination of active faults and mapping of the microearthquake activity. Therefore, to recognize the tectonic activity in the region, we need to be able to discriminate between earthquakes and quarry blasts in the catalogues. In this study, a statistical analysis method (linear discriminant function) has been applied to classify seismic events occurring in the Sakarya region. We used 110 seismic events that were recorded by Sakarya University Seismic Station between 2012 and 2014. Time and frequency variant parameters, maximum S wave and maximum P wave amplitude ratio (S/P), the spectral ratio (Sr), maximum frequency (fmax), and total signal duration of the waveform were used for discrimination analyses. The maximum frequency (fmax) versus time duration of the seismic signal gives a higher classification percentage (94%) than the other discriminants. At the end of this study, 41 out of 110 events (44%) are determined as quarry blasts, and 62 (56%) are considered as earthquakes.  相似文献   

15.
—The 12 November 1996 M w 7.7 Peru subduction zone earthquake occurred off the coast of southern Peru, near the intersection of the South American trench and the highest topographical point of the subducting Nazca Ridge. We model the broadband teleseismic P-waveforms from stations in the Global Seismic Network to constrain the source characteristics of this subduction zone earthquake. We have analyzed the vertical component P-waves for this earthquake to constrain the depth, source complexity, seismic moment and rupture characteristics. The seismic moment determined from the nondiffracted P-waves is 3–5 × 1020 N·m, corresponding to a moment magnitude M w of 7.6–7.7. The source time function for the 1996 Peru event has three pulses of seismic moment release with a total duration of approximately 45–50 seconds. The largest moment release occurs at approximately 35–40 seconds and is located ～90km southeast of the rupture initiation. Approximately 70% of the seismic moment was released in the third pulse.¶We find that the 1996 event reruptured part of the rupture area of the previous event in 1942. The location of the 1996 earthquake corresponds to a region along the Peru coast with the highest uplift rates of marine terraces. This suggests that the uplift may be due to repeated earthquakes such as the 1996 and 1942 events.  相似文献   

16.
In this study, seismic data recorded during the period 01/01/1996 to 09/01/2009 has been used to evaluate the seismic hazard potential along the Alborz region, Northern Iran. The technique of mapping local recurrence time, T L, is used to map major asperities, which are considered as the areas with maximum hazard. We calculated T L from a and b values which are in turn derived from the frequency–magnitude relation constants within a radius of 30 km about every corner point of a 10-km spacing grid. Since b value is inversely related to applied stress, the areas with lowest b values and/or shortest T L are interpreted to locate the asperities or the areas of maximum seismic hazard. To test this method, we computed T L map using seismic catalogues before and after the 2004 Baladeh earthquake of M w 6.2. The local recurrence time map before the earthquake shows anomalously short T L in the epicentral region of the Baladeh earthquake a decade before its occurrence. The T L map after the earthquake indicates that this large event has redistributed the applied stress in the Alborz region. The microseismicity of the region after the Baladeh earthquake, however, suggests that there are two anomalies in T L map positioned in Alborz. The places where these anomalies are observed can be considered as the areas with maximum seismic hazard for future large earthquake in the Alborz region.  相似文献   

17.
The paper summarizes the findings about a seismic event on January 22, 2010, near Bełchatów, Poland, in terms of data, event location, magnitude and source parameters.  相似文献   

18.
The earthquake of February 1 (January 21 in the Julian Calendar), 1725 was for a long time considered not only the earliest precisely dated historical seismic event in eastern Siberia, but also the most powerful earthquake for the entire period of recorded seismic events in the region: M = 8.2 (Novyi katalog…, 1977). The epicenter location (Stanovoy Upland) and the magnitude of the event were assessed on the basis of very scanty historical data, as well as using paleoseismogeological information. The February 1, 1725 event received the name “The Great East Siberian” earthquake and served for decades as decisive evidence for the assessment of the seismic hazard and seismic zoning of the northeastern flank of the Baikal rift zone. However, the solution of the focal parameters in the (Novyi katalog…, 1977) has caused serious doubts. In this paper a newly elaborated version is proposed that is based on a detailed reevaluation of the initially known macroseismic information, as well as additional historical data that previously had not come to the attention of seismologists. As the result, a different solution of the focal parameters (51.8° N; 113.0° E, eastern Transbaikalia) and a significantly lower magnitude (M = 6.0) compared with the parameters given in (Novyi katalog…, 1977) were obtained. The presented solution makes us more attentive to the estimates of seismic hazard in east Transbaikalia based on historical data, as well as to the historical data themselves.  相似文献   

19.
We present the main seismological results of our study of the Campania-Lucania earthquake of 23 November 1980. A complete set of far field and local data has been analysed. From long-period body waves data we determine the fault plane solution (φ1 = 140°,δ1 = 60°,φ2 = 75°,δ2 = 54°), a depth of 15 km and calculate a seismic moment of 6 × 1025 dyne cm and a source duration of 6 s. From data of a local network deployed immediately after the event we determine aftershock locations: they are aligned in a direction NW-SE that fit extremely well with the focal solution determined above. We can choose as fault plane the plane striking 140° and dipping at 60° and the event is a normal event with a large component of left-lateral strike slip. The source area evaluated from this aftershock distribution 14 km × 40 km is quite suitable for an earthquake of a seismic moment of 6 × 1025 dyne cm.  相似文献   

20.
We investigate mainshock slip distribution and aftershock activity of the 8 January 2013 M w?=?5.7 Lemnos earthquake, north Aegean Sea. We analyse the seismic waveforms to better understand the spatio-temporal characteristics of earthquake rupture within the seismogenic layer of the crust. Peak slip values range from 50 to 64 cm and mean slip values range from 10 to 12 cm. The slip patches of the event extend over an area of dimensions 16?×?16 km2. We also relocate aftershock catalog locations to image seismic fault dimensions and test earthquake transfer models. The relocated events allowed us to identify the active faults in this area of the north Aegean Sea by locating two, NE–SW linear patterns of aftershocks. The aftershock distribution of the mainshock event clearly reveals a NE–SW striking fault about 40 km offshore Lemnos Island that extends from 2 km up to a depth of 14 km. After the mainshock most of the seismic activity migrated to the east and to the north of the hypocenter due to (a) rupture directivity towards the NE and (b) Coulomb stress transfer. A stress inversion analysis based on 14 focal mechanisms of aftershocks showed that the maximum horizontal stress is compressional at N84°E. The static stress transfer analysis for all post-1943 major events in the North Aegean shows no evidence for triggering of the 2013 event. We suggest that the 2013 event occurred due to tectonic loading of the North Aegean crust.  相似文献   

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