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1.
A method for the evaluation of seismic hazard in a given zone, taking into account both the spreading of macroseismic effects and seismic catalogue information, is applied. A data-bank of some 500 digitized isoseisms of earthquakes having occurred in Italy between 1542 and 1986 is used. The isoseismical maps are digitized considering for each degree of intensity the length of 24 spreading rays starting from the macroseismic epicenter or barycentre of the megaseismic area. These rays are separated from each other by the same angle, i.e. every isoseism is divided into 24 equal circular sectors. The year 1542 is taken as the beginning of the time span, since this is when the first seismic event occurred for which reliable isoseismal maps are available. The epicentral intensities considered lie between theVI andXI degrees of the Mercalli-Cancani-Sieberg scale (MCS). This digitized data-bank is analyzed to achieve, for each homogeneous seismogenetic zone that has been recognized, the mean azimuthal spreadings of effects for each degree of intensity as a function of the epicentral intensity. Once a mean propagation model is obtained for each zone, this is applied to seismic events of the same zone, the isoseismal maps of which are not available. A geographic grid is defined to cover the analyzed area, and for each cell of this grid it is then possible to count the number of felt events and their degree. These effects have been evaluated either on the basis of the isoseismal maps (when available) or on the basis of the mean propagations of the zone in which the single event occurred. Moreover, an index summarizing the seismic information was computed for each cell of the previous grid. All the events producing effects and their provenance are stored on files, allowing the main seismogenic zones influencing this cell to be identified. This methodology has been applied to central and southern Italy in an area between the latitudes 40.6 and 43.3 N. In particular, attention is focussed on the sample areas of Rome (given the historical and political importance of the city) and of the Sannio-Matese and Irpinia zone (in which some of the strongest earthquakes of the Apennine chain have occurred). Finally, in order to evaluate the maximum expected magnitude, extreme value statistics (Gumbel III-type) are applied to the Colli Albani area, which represents the seismogenic zone nearest to Rome. For the Sannio-Matese and Irpinia area, considering the more dangerous zone as a unicum, theWeibull distribution has been hypothesized to determine the mean return time for events with an intensity greater than or equal to IX.  相似文献   

2.
A. Pantea 《Natural Hazards》1994,10(1-2):65-72
The macroseismic intensity attenuation (m.i.a.) laws for the main seismic provinces with crustal foci of the Romanian territory and adjacent areas were established. The input data consist of MSK-64 intensities of 18 earthquakes with epicentral/maximum intensity in the range V to X degrees (MSK scale), whose isoseismal maps were available.The attenuation was analyzed as a function of distance and azimuth and from the three main attenuation formulas (logarithmic, exponential, and power-law) (the last one was preferred, as it best fits the observed data) and, consequently, were used for each seismogenic region. The bulk of derived equations is intended to be further used in the assessment of the seismic hazards of Romania.  相似文献   

3.
The SIRENE macroseismic database has been utilized to draw isoseismal maps for the 140 best-documented French earthquakes, characterized by epicentral intensities of at least V (MSK) and located in all parts of the country. A study of focal depths derived from available local intensity data using an intensity versus distance decay law (Sponheuer) shows that the focal depths of most of the events considered do not exceed about 10 km. Their distribution correlates fairly well with regional dynamic geology features. A relationship is then computed between magnitude, intensity and focal distance, based on 73 instrumenta]ly recorded earthquakes (M L between 3.3 and 6.3) and on 217 mean radius values (from 2 to 380 km) for isoseismals of intensity VIII to III (MSK). This relationship is applied to historical earthquakes contained in the database SIRENE which are characterised by their intensity only. These results are used in the evaluation as well deterministic as probabilistic of the seismic hazard on the national territory.  相似文献   

4.
This paper both describes and discusses landslides and other ground effects induced by the September–October 1997 seismic sequence, which struck the Umbria and Marche regions (Central Italy). Three main events occurred on 26 September at 00:33 and 09:40 GMT, and 14 October with magnitude Mw equal to 5.8, 6.0 and 5.4, respectively; furthermore hundreds of minor but significant events were also recorded. The authors examined an area of some 700 km2 around the epicentre (Colfiorito). Primary and secondary effects were observed, including surface faulting phenomena, landslides, ground fractures, compaction and various hydrological phenomena. Surface evidence of faulting reactivation was found along the well-known capable faults, to a total length of ca. 30 km. Landslides, which were the most recurrent among the phenomena induced, consisted mainly of rock falls and subordinately of rotational and translational slides, which were generally mobilised by the inertia forces during the seismic motion. The percentage of reactivated old landslides decreased as the distance from the epicentral zone increased; a similar decrease had been observed for the 1980 Irpinia earthquake (Southern Italy). The ground fracture distribution was consistent with the regional structural setting and the general pattern of macroseismic field. Numerous episodes of hydrological changes were observed within the most severely damaged area. All this evidence confirms the relevance of the study of ground surface effects for achieving a more complete evaluation of seismic hazard.  相似文献   

5.
The seismic hazard in the Sannio-Matese area has been worked out by a modification of the McGuire (1976) computing programme, taking into account the influence of nine potential seismic source zones.The method uses truncated-quadratic intensity-frequency distribution and azimuth-dependent intensity attenuation derived from isoseismal maps for each of the seismogenetic sources. A new modification has been introduced to take into account different decay of the intensity in the near (to VIII degree) and far (from VIII degree) field.Different assumptions about maximum possible intensities and truncation of intensity-frequency laws are used to evaluate the effects of the uncertainties on the computed hazard at high intensities. Intensities associated with different level of annual probability are computed for five test sites in the considered area. Maps displaying the expected intensity for a mean return period of 500 years (pa 0.002) are presented and compared with observed intensities.Presented at the XXIst General Assembly of the European Seismological Commission, Symposium on Methods of Seismic Hazard Assessment in Europe, Sofia, 23–27 August 1988.  相似文献   

6.
The assessment of seismic hazard at five selected sites in the Sannio-Matese region is based on the computer program SRAMSC. Owing to the extensive historical data base for the output parameter, the MSK intensiy is chosen. The seismicity model is made up of five narrow area seismic sources. Circular or elliptical macroseismic fields are assigned to individual sources. A generalized Kövesligethy equation is used for this purpose as the attenuation relationship. The study reveals similar and a rather high hazard at the sites at Benevento, Boiano, and Melfi, which are located in the zone of highest seismic activity. At the Pomigliano and Lucera sites, the assessed hazard is much lower.  相似文献   

7.
In this study, we have prepared an intensity map based on macroseismic survey and all the available information from print and electronic media of damage and other effects due to March 05, 2012, M 4.9 Bahadurgarh (Haryana–Delhi border) earthquake and interpreted them to obtain modified Mercalli intensities (MMI) at over 62 locations surrounding the Haryana and Delhi. We have cross-checked the damage information from print and electronic media in the field at 25 sites within 110 km surrounding the epicenter for validation. Based on the questionnaire which is used in macroseismic survey and personal judgment, intensities were assigned accordingly as per physical survey at 25 sites and for rest based on media reporting. A maximum intensity of VI was assigned to this seismic event. Isoseismals of V and VI have been fully covered in the field observations. Beside this, some of the points have also been covered for isoseismal IV and isoseismal III and rest are based on media report only. The intensity map reveals several interesting features. Elliptically elongated shape of intensity map shows that most of the slightly damaged areas are concentrated toward the northwestern side of the epicenter having intensity V which may be due to directivity or site effects. A regression relation has also been derived between intensity and epicentral distance. The derived attenuation relation will be useful for assessing damage of a potential future earthquake (earthquake scenario–based planning purposes) for the Delhi NCR region.  相似文献   

8.
A semi-probabilistic approach to the seismic hazard assessment of Greece is presented. For this reason, a recent seismotectonic model for shallow and intermediate depth earthquake sources, based on historical as well as on instrumental data, was used. Different attenuation formulae were proposed for the macroseismic intensity and the strong ground motion parameters for the shallow and the intermediate focal depth shocks. The data were elaborated in terms of McGuire's computer program, which is based on the Cornell's method.A grid of equally spaced points at 20 km distance was made and the seismic hazard recurrence curves for various parameters of the seismic intensity was estimated for each point. Finally, seismic hazard maps for the area of Greece were compiled utilizing the entire range of recurrence curves. These maps depict areas of equal seismic hazard and for every area the analytical relations of the typeSI =f(Tm), whereSI is a seismic intensity parameter andTm is the mean return period, were determined.  相似文献   

9.
Many moderate events reported by Italian earthquake catalogues (either historical or recent) are listed with an epicentral intensity derived from intensitymagnitude relationships or evaluated based on preliminary sources. Contradictions may arise among different catalogues when the effects of a given earthquake are not assessed through a specific macroseismic study as each catalogue generally uses its own criteria for evaluating the intensity. In this paper we present the case of the June 19 1975 earthquake, a ML = 5.1 (ING seismological bulletin) event that occurred in the Gargano area (southern Italy). The intensity reported by the ING catalogue is VIII MCS (estimated from magnitude), that reported by the NT4.1 catalogue is VI MCS, while the PFG catalogue does not report an intensity. The case of this event is well representative of a period during which macroseismic studies were not undertaken systematically in Italy. In this paper we reassess the macroseismic intensity of this event using procedures implemented and routinely used at ING.  相似文献   

10.
For two different zonations of the Calabro-Sicilian region the macroseismic intensity attenuation parameters are computed using the Grandori model.Some modifications to this relation are proposed here in order to allow its applicability also to those cases in which the data set available for each source zone does not present three successive epicentral intensity levels (I 0) as required for its application.Maps of theoretical distribution of maximum expected intensities were plotted for both zonations adopted, in order to test the reliability, also using other attenuation models.The results of the analysis show how the proposed modifications to the Grandori relation allow the macroseismic intensity attenuation modelling even in cases in which only one intensity level is available.Finally, the comparison of theoretical maximum expected intensity distribution maps, computed for different attenuation models and seismogenic zonations, shows that the maps plotted using the Grandori model and the zonation adopted by G.N.D.T. (Gruppo Nazionale Difesa dai Terremoti - C.N.R. Italy) are more reliable.  相似文献   

11.
Teramo  A.  Termini  D.  Stillitani  E.  Bottari  A. 《Natural Hazards》1998,17(1):17-29
The anisotropic attenuation of macroseismic intensity for a seismogenetic zone is dealt with using a new modelling of intensity distribution. The analysis, carried out starting from the intensity maps of the earthquakes of different seismogenetic zones of Central and Southern Italy, allows the determination of the attenuation coefficients for each seismogenetic zone by an anisotropic attenuation law. The obtained results show the reliability of the proposed modelling within seismic hazard evaluation studies.  相似文献   

12.
Acceleration and velocity data of large earthquakes recorded by the Mexican National Broadband Seismological Network were used to generate isoseismal maps for Mexico. The seismic data consist of 99 events recorded at 27 seismic stations located in the southern and northern regions of Mexico from 2004 to 2009. The magnitude (Mw) of these events ranged from 4.1 to 7.1. Peak ground velocity values (PGV) and peak ground accelerations (PGA) were estimated, and velocity-derived peak ground accelerations (PGAv) were calculated. No important differences between PGAv and PGA values were found; thus, both parameters were used in the isoseismal determination. The generated synthetic isoseismal maps were compared with those from an existing catalog for large earthquakes in Mexico. Using empiric relations between PGA and MMI (modified Mercalli intensity) and PGV and MMI, the obtained simulated intensity maps showed similar behavior to those reported in the catalog. The results indicate that the PGAv values can be used to determine intensities when acceleration records (PGA) are unavailable.  相似文献   

13.
It is shown that the foci of the recent earthquakes in the Thessaloniki area of northern Greece are located in an arcuate seismic zone which is associated with the Serbomacedonian geologic zone. Three main lines of fracture have been observed in the epicentral area after the May–June 1978 earthquakes. Field and macroseismic observations as well as fault plane solutions for the main shock and for the largest foreshock show that both earthquakes are due to a strike slip sinistral motion with a small reverse component on a steeply dipping and trending southeast-northwest fault.  相似文献   

14.
Compilation of the digital Croatian Macroseismic Database is an ongoing project that started in 1995. Final version of the database will contain all the macroseismic data from the archive of the Department of Geophysics (including data for neighboring countries) without time or intensity threshold. The database has two subsets: intensity point database and the digital archive. A total of 426 earthquakes felt in Croatia are currently being analyzed. The job is carried out through several stages, each of them corresponding to digitalization of a different input data format (intensity maps, intensity point lists, questionnaires, etc.). 69 intensity maps of the earthquakes felt in Croatia, published in the Catalogue of Earthquakes in the Balkan Region were digitized first. The coordinates of intensity points were assigned to geographic locations (villages, cities, …) by consulting the database of latitudes and longitudes of all settlements in Croatia (database of settlements). 330 existing intensity lists (intensity and name of the place without coordinates) were entered into the database during the second step. The intensity maps which were not published so far will be scanned and digitized during the third stage of the project. The last stage will be input of primary data to the digital archive and reassessing of intensities according to the EMS macroseismic scale. The main goal of this paper is to describe the way of database compilation. Preliminary felt intensity map and number of intensity points map illustrate possibilities of macroseismic field analyze.  相似文献   

15.
Short communication: collection of isoseismal maps for South Africa   总被引：1，自引：0，他引：1  
An atlas of isoseismal maps for South Africa, dating from as far back as 1932–2005, is provided. This work involved searching through historical reports to find records of macroseismic effects. In many instances, when there was a large tremor, questionnaires were distributed to local towns to assess the severity of the tremor and the damage it caused. Based on the results of these questionnaires and site investigations, isoseismal maps were drawn. These isoseismal maps were revisited and digitised for this study. Five additional isoseismal maps were prepared by the authors based on the results of questionnaires alone. Most isoseismal maps in the historical record use the Modified Mercalli scale. All maps are hence provided according to this scale. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

16.
A study concerning the multiplicity character of Vrancea earthquake of March 4, 1977 based on records of the Romanian seismic network is presented. Four separate shocks within a 9 s interval were recognized of which three with M = 6.0–6.9. Some explanations regarding the macroseismic intensity are made. Also analysed are the shaking duration, the influence of the Carpathian Mountains on the shape of the isoseismal curves and the focal mechanism for the first two main shocks.  相似文献   

17.
In this paper we present magnitude (Ms) – magnitude(mb) and magnitude-intensity relationships which areconsidered the most adequate in the Ibero-Maghrebianregion. This work is based on selected samples ofrecently revised events with magnitude mb assigned bythe Instituto Geográfico Nacional (I.G.N.) and Msassigned by I.S.C and N.E.I.C., and isoseismal mapsfrom 142 events. Using these data, we have obtainedone magnitude (Ms) – magnitude (mb) relationship, twomagnitude (mb and Ms) assignment relationships viaepicentral intensity (I0), and ten magnitude (mb andMs) assignments relationships via macroseismicinformation: four using Ambraseys' methodology (1985)and six using the isoseismal area of degree III, IV and VI.According to the obtained results it could be concluded that historical magnitude assignment with lesser uncertainties are those obtained via macroseismic information using magnitude-intensity relationships with Ambraseys' methodology (1985). The magnitude-isoseismal area assignment relationships have, in most cases, great differences depending on the degree of the isoseismal area used. Magnitude assignments via epicentral intensity have the highest uncertainties. Geographic regionalization of the relationshipshas been studied but the highest correlations and statistical significance are obtained when we fit all the Ibero-Maghrebian region data.Finally we have used the results obtained in this workto assign magnitude to some important historicalearthquakes in the Ibero-Maghrebian region: the 1755Lisbon earthquake, the 1680 Málaga earthquake, the1829 Torrevieja earthquake and the 1884 Arenas del Reyearthquake. According to our relationships andmethodology we have assigned an Ms value of 9.3 ±0.6 to the 1755 Lisbon earthquake (its mb magnitudecannot be estimated due to the saturation of the mbscale), an mb value of 6.3 ±0.4 and an Ms valueof 6.9 ± 0.6 to the 1829 Torrevieja earthquake, anmb value of 6.2 ± 0.4 and an Ms value of 6.4 ±0.6 to the 1680 Málaga earthquake and an mb valueof 6.1 ± 0.4 and an Ms value of 6.5 ± 0.6 tothe 1884 Arenas del Rey earthquake.  相似文献   

18.
Several seismogeological effects of earthquakes on the environment have been collected by means of the ING macroseismic procedure. The fast and easy collection of information about ground and hydrological effects constitutes a complementary instrument in assessing the effects on human structures and the environment, and, ultimately, establishing intensity values. In this paper the distribution of seismogeological effects within intensity values has been verified, using data from three moderate Italian earthquakes; the density of the same effects are then discussed in comparison with isoseismal maps.  相似文献   

19.
《Geodinamica Acta》1999,12(3-4):179-191
The study of growth anomalies of speleothems in a karstic environment can provide potential evidence for palaeoearthquakes. These data are used to study the recurrence times of major earthquakes in areas where evidence for historic seismicity is lacking. A study has been carried out in the epicentral area of the 1356 Basel earthquake (epicentral intensity = VII–VIII, macroseismic magnitude = 6.2). The Bättlerloch and Dieboldslöchli caves, situated in the area of greatest damage, show growth anomalies of speleothems possibly related to a seismic event (several breaks of speleothems and offsets of the axis of the regrowths). The first U/Th disequilibrum measurements by alpha spectrometry show recent ages (less than several tens of thousands of years and probably historic). 14C dating by AMS of carbonate laminations taken on both sides of the anomalies confirm the evidence of a seismic event around 1300 AD. More accurate darings by U/Th TIMS are carried out in order to compare the information provided by the two different dating methods.  相似文献   

20.
Within the activity of the ESC Subcommission 8 Engineering Seismology, Project TERESA, seismic hazard calculations have been performed for two areas of a different earthquake activity. Fundamental seismological data (earthquake catalogues, macroseismic observations and maps) and some additional geological information were analyzed and processed to prepare inputs for hazard computations. Great attention has been paid to verifying the reliability of the input data. Seismic hazards obtained for five sites of the region of high seismic activity (Sannio-Matese, southern Italy) and six sites of the region of low seismic activity (Brabant Massif and northern Rhine, Belgium—The Netherlands—Germany) are presented and discussed.  相似文献   

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