共查询到10条相似文献,搜索用时 140 毫秒
1.
Dmitry A. Storchak 《Physics of the Earth and Planetary Interiors》2006,158(1):4-13
The International Seismological Centre (ISC) is charged with production of the definitive global bulletin of seismic events, based on the most comprehensive set of parametric data collected from all over the world. Almost every event in the bulletin retains the original hypocentral solutions reported to the ISC by contributing agencies. In addition, where possible, the ISC computes its own solution, which is intended to be the most accurate where the data from several networks are used. It is because of the requirement for consistency of the bulletin over the years that the procedures used at the centre to compute hypocentres have remained rather conservative despite considerable advances made in the field of earthquake location.The ISC has developed and put into operation a new data management system. As a result, it is now possible to review and subsequently introduce more up-to-date methods of locating seismic events into the operations. The ISC Governing Council called for a workshop dedicated to location procedures, which was held during the 2005 IASPEI General Assembly in Santiago, Chile.To compare the accuracy of different location algorithms, a list of 156 reference events (IWREF) was selected prior to the workshop. The list includes geographically well distributed earthquakes and explosions with positions known with an accuracy of up to 5 km. It covers the period of 1954-2001 and includes all station readings and hypocentral solutions of different agencies available for these events in the ISC bulletin. Although the original ISC solutions are included, these may be different from the solution obtainable now due to changes in the ISC procedures over the years. This paper presents the results of relocation of these events using standard ISC location procedures as of 2005. These new ISC locations and analysis of their shifts with respect to reference locations present a benchmark for further improvement. 相似文献
2.
V. Pinsky 《Physics of the Earth and Planetary Interiors》2006,158(1):75-83
The aim of this study is the design and trial of a novel sparse network beamforming (NB) technique to improve earthquake location. For this purpose bulletin phase arrival time data were processed via the use of complex exponents form and then used in an optimization via grid-search to search for the maximum semblance in hypocenter space. The use of the robust semblance statistic, provides reliable location results. The NB location results for a set of test events were compared to standard iterative ISC location procedure “iscloc” and its prototype the Jeffreys maximum likelihood estimator. For this purpose a data-base of 139 reference ground-truth events was extracted from the catalog of the International Seismological Centre (ISC) (97 GT5 events, assumed earthquakes, and 42 GT0 nuclear tests). The tuned NB procedure has shown excellent location results for events with a “good” ISC location and demonstrated the large epicenter deviations have been decreased in “bad” cases. Further developments of the algorithm would include allowances for 3D earth structure and a priori site-specific information. 相似文献
3.
Maiclaire K. Bolton Dmitry A. Storchak James Harris 《Physics of the Earth and Planetary Interiors》2006,158(1):27-45
The International Seismological Centre (ISC) publishes the definitive global bulletin of earthquake locations. In the ISC bulletin, we aim to obtain a free depth, but often this is not possible. Subsequently, the first option is to obtain a depth derived from depth phases. If depth phases are not available, we then use the reported depth from a reputable local agency. Finally, as a last resort, we set a default depth.In the past, common depths of 10, 33, or multiples of 50 km have been assigned. Assigning a more meaningful default depth, specific to a seismic region will increase the consistency of earthquake locations within the ISC bulletin and allow the ISC to publish better positions and magnitude estimates. It will also improve the association of reported secondary arrivals to corresponding seismic events.We aim to produce a global set of default depths, based on a typical depth for each area, from well-constrained events in the ISC bulletin or where depth could be constrained using a consistent set of depth phase arrivals provided by a number of different reporters.In certain areas, we must resort to using other assumptions. For these cases, we use a global crustal model (Crust2.0) to set default depths to half the thickness of the crust. 相似文献
4.
文中使用了一个新的量规函数σ300(Δ),它是基于面波传播理论,考虑了面波的几何扩散、非弹性吸收、频散衰减以及面波优势周期随震中距的变化导出的,取全球平均Q=300。在震中距Δ=20°-160°的范围内与IASPEI推荐的面波震级的量规函数σIASPEI(Δ)一致,又推广了σIASPEI(Δ)的震中距使用范围,从1.0°-179°,以及可使用的面波周期范围(7.5-30s),因此它更适合我国由中周期宽频带SK仪组成的台网情况。若采用此量规函数σ300(Δ)和进行方位角改正,则可使我国台网测出的Ms与国际地震中心(ISC)测出的一致,震级误差降到0.19级,此误差与苏联台网的误差一样。 相似文献
5.
J. Schweitzer 《Pure and Applied Geophysics》2001,158(1-2):375-396
—?The first step to identify and locate a seismic event is the association of observed onsets with common seismic sources. This is especially important in the context of monitoring the Comprehensive Nuclear-Test-Ban Treaty (CTBT) at the International Data Center (IDC) being developed in Vienna, Austria. Well-defined slowness measurements are very useful for associating seismic phases to presumed seismic events.¶Shortly after installation of the first seismic arrays, systematic discrepancies between measured and theoretically predicted slowness values were observed, and therefore slowness measurements of seismic stations should be calibrated. The observed slownesses measured with small aperture arrays, some of which will be included in the International Monitoring System (IMS) now being implemented for verifying compliance with the CTBT, show large scatter and deviations from theoretically expected values. However, in this study a method is presented, by which mean slowness corrections can be derived, which show relatively stable patterns specific to each array.¶The correction of measured slowness values of these arrays clearly improved the single array location capabilities. Applying slowness corrections with seismic phases observed by ARCES, FINES, GERES, and NORES, and associated to seismic events in the bulletins of the prototype International Data Center (pIDC) in Arlington, VA, also clearly demonstrates the advantages of these corrections. For arrays with large slowness deviations that are due to the influence of a dipping layer, the corrections were modeled with a sine function depending on the measured azimuth. In addition, the measured values can be weighted with the corresponding uncertainties known from the process of deriving the mean corrections. 相似文献
6.
The Kirovskiy Explosion of September 29, 1996: Example of a CTB Event Notification for a Routine Mining Blast 总被引:3,自引:0,他引:3
—?On September 29, 1996, a routine mining blast of about 390 metric tons was detonated underground at the Kirovskiy mine in the central Kola Peninsula. The United States was notified two weeks in advance that the blast was to take place and was given the date, approximate time, location and total charge. The explosion was detected and located by the prototype International Data Center (pIDC) and published in the Reviewed Event Bulletin (REB). Detailed information about the blast, including the type and depth of mining operation, the underground charge configuration, and the blasting delay pattern, is reviewed and combined with a seismological analysis of the event. The seismic analysis points to a possible associated tectonic component to the blast, consisting of a small rock burst or induced tremor, spall, or some combination of these mechanisms, that may have enhanced the shear waves, produced large Rg waves at low frequency, and small Pn/Sn and Pn/Lg amplitude ratios at high frequency. While these discriminants might identify the event as an earthquake, the spectral/cepstral analysis of the event clearly shows the ripple-fire delays. This event provides important confidence-building measures for both location calibration, in the form of travel-time corrections for location of mine events in this region, and for improved understanding of seismic discriminants expected for large mine blasts that may have an associated induced tectonic component (e.g., spall, mine tremor or rock burst). 相似文献
7.
《中国地震研究》2016,(1)
The Haicheng-Xiuyan region is an earthquake-prone area in Liaoning Province where earthquake sequences frequently occur and is regarded as the regional seismic window. In this area we found many earthquake events with the highest waveform similarity in the records of the same station from some remarkable seismic sequences,namely repeating earthquake sequences. In principle,rupture areas of the repeating events overlap with each other and are most closely located. Therefore these events may reflect the seismic process near the earthquake fault. In this paper, we identified four remarkable earthquake sequences of Haicheng-Xiuyan by waveform cross-correlation. The result shows that the cumulative slip of repeating earthquakes is related to moderately strong earthquakes,among which the Xiuyan M_S5. 4 foreshock sequence has the strongest and most apparent pre-shock accelerating-like slip behavior. 相似文献
8.
One of the main purposes of the International Seismological Centre (ISC) is to collect, integrate and reprocess seismic bulletins provided by agencies around the world in order to produce the ISC Bulletin. This is regarded as the most comprehensive bulletin of the Earth’s seismicity, and its production is based on a unique cooperation in the seismological community that allows the ISC to complement the work of seismological agencies operating at global and/or local-regional scale. In addition, by using the seismic wave measurements provided by reporting agencies, the ISC computes, where possible, its own event locations and magnitudes such as short-period body wave m b and surface wave M S . Therefore, the ISC Bulletin contains the results of the reporting agencies as well as the ISC own solutions. Among the most used seismic event parameters listed in seismological bulletins, the event magnitude is of particular importance for characterizing a seismic event. The selection of a magnitude value (or multiple ones) for various research purposes or practical applications is not always a straightforward task for users of the ISC Bulletin and related products since a multitude of magnitude types is currently computed by seismological agencies (sometimes using different standards for the same magnitude type). Here, we describe a scheme that we intend to implement in routine ISC operations to mark the preferred magnitudes in order to help ISC users in the selection of events with magnitudes of their interest. 相似文献
9.
We analyzed the International Seismoogical Center(ISC)catalogue of seismologil publicationsfrom 1980 to 1995 to investigate how much infonformation provided by an earithquake hes beenutilized to obtain a better undertanding of earthauakes and selsmic disaster.We sekect the ISCbulletin which has a wider coverage of seismological journals and languages than the ScientificCitation Index(SCI),so that there is less regional or language bias in the analysis.The earth-quakes in the catalogue span the period from 1975 to 1990.Papers which have direct relationwith an earthquake as defined by the ISC catalogue range from 1 to 10~2 in order of magni-tudes.The logarithm of the maximum number of papers on an earthquake is shown to be prop-ortional to the magnitude of the earthquake,which provides a possibility to define a“normali-zed impact strength”of an earthquake,so that earthquakes with different magnitudes can becompared with each other.Magnitude span of the earthquakes with a certain“impact strengthlevel”an 相似文献
10.
The source process of the deep-focus Spanish earthquake of March 29, 1954 (mb = 7.1, h = 630 km) has been studied by using seismograms recorded at teleseismic distances. Because of its unusual location, this earthquake is considered to be one of the most important earthquakes that merit detailed studies. Long-period body-wave records reveal that the earthquake is a complicated multiple event whose wave form is quite different from that of usual deep earthquakes. The total duration of P phases at teleseismic distances is as long as 40 s. This long duration may explain the considerable property damage in Granada and Malaga, Spain, which is rather rare for deep earthquakes. Using the azimuthal distribution of the differences between the arrival times of the first, the second and later P phases, the hypocenters of the later events are determined with respect to the first event. The focus of the second event is located on the vertical nodal plane of the first shock suggesting that this vertical plane is the fault plane. This fault plane which strikes in N2°E and dips 89.1°E defines a nearly vertical dip-slip fault, the block to the west moving downwards. The time interval and spatial separation between the first and the second events are 4.3 s and 19 km respectively, giving an apparent rupture velocity of 4.3 km/s which is about 74% of the S-wave velocity at the source. A third event occurred about 8.8 s after the first event and about 35.6 km from it. At least six to ten events can be identified during the whole sequence. The mechanism of some of the later events, however, seems to differ from the first two events. Synthetic seismograms are generated by superposition of a number of point sources and are matched with the observed signals to determine the seismic moment. The seismic moments of the later events are comparable to, or even larger than, that of the first. The total seismic moment is determined to be 7 · 1027 dyn cm while the moments of the first and the second shocks are 2.1 · 1026 dyn cm and 5.1 · 1026 dyn cm, respectively. The earthquake may represent a series of fractures in a detached piece of the lithosphere which sank rapidly into the deep mantle preserving the heterogeneity of material property at shallow depths. 相似文献