International Seismological Center

Thatcham, United Kingdom

International Seismological Center

Thatcham, United Kingdom

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Bormann P.,German Research Center for Geosciences | Di Giacomo D.,German Research Center for Geosciences | Di Giacomo D.,International Seismological Center
Journal of Seismology | Year: 2011

Starting from the classical empirical magnitude-energy relationships, in this article, the derivation of the modern scales for moment magnitude Mw and energy magnitude Me is outlined and critically discussed. The formulas for Mw and Me calculation are presented in a way that reveals, besides the contributions of the physically defined measurement parameters seismic moment M0 and radiated seismic energy ES, the role of the constants in the classical Gutenberg-Richter magnitude-energy relationship. Further, it is shown that Mw and Me are linked via the parameter Θ = log(ES/M0), and the formula for Me can be written as Me = Mw + (Θ + 4.7)/1. 5. This relationship directly links Me with Mw via their common scaling to classical magnitudes and, at the same time, highlights the reason why Mw and Me can significantly differ. In fact, Θ is assumed to be constant when calculating Mw. However, variations over three to four orders of magnitude in stress drop Δσ (as well as related variations in rupture velocity VR and seismic wave radiation efficiency ηR) are responsible for the large variability of actual Θ values of earthquakes. As a result, for the same earthquake, Me may sometimes differ by more than one magnitude unit from Mw. Such a difference is highly relevant when assessing the actual damage potential associated with a given earthquake, because it expresses rather different static and dynamic source properties. While Mw is most appropriate for estimating the earthquake size (i. e., the product of rupture area times average displacement) and thus the potential tsunami hazard posed by strong and great earthquakes in marine environs, Me is more suitable than Mw for assessing the potential hazard of damage due to strong ground shaking, i. e., the earthquake strength. Therefore, whenever possible, these two magnitudes should be both independently determined and jointly considered. Usually, only Mw is taken as a unified magnitude in many seismological applications (ShakeMap, seismic hazard studies, etc.) since procedures to calculate it are well developed and accepted to be stable with small uncertainty. For many reasons, procedures for ES and Me calculation are affected by a larger uncertainty and are currently not yet available for all global earthquakes. Thus, despite the physical importance of ES in characterizing the seismic source, the use of Me has been limited so far to the detriment of quicker and more complete rough estimates of both earthquake size and strength and their causal relationships. Further studies are needed to improve ES estimations in order to allow Me to be extensively used as an important complement to Mw in common seismological practice and its applications. © 2010 Springer Science+Business Media B.V.

Storchak D.A.,International Seismological Center | Kanao M.,Japan National Institute of Polar Research | Kanao M.,Graduate University for Advanced Studies | Delahaye E.,International Seismological Center | Harris J.,International Seismological Center
Polar Science | Year: 2015

The International Seismological Centre (ISC) is a non-governmental non-profit making organization funded by 62 research and operational institutions around the world and charged with the production of the ISC Bulletin - the definitive summary of the global seismicity based on reports from over 130 agencies worldwide, including those active in Polar regions. Jointly with the National Earthquake Information Center (NEIC) of the United States Geological Survey (USGS), the ISC runs the International Seismic Station Registry. The ISC is also charged with maintaining the International Association of Seismology and Physics of the Earth Interior (IASPEI) Reference event List. The new ISC product, the ISC Event Bibliography allows users to obtain references to scientific articles describing specific seismic events, natural and anthropogenic. In this paper we demonstrate how these products and services are applicable to seismic events both in Arctic and Antarctic regions. We also give a summary of the ISC data in polar regions and provide credit to Institutions that report these data to the ISC. © 2014 Elsevier B.V. and NIPR.

Chen S.,International Seismological Center | Chen S.,Nanjing University | Chen S.,Geomatrix Consultants
Bulletin of the Seismological Society of America | Year: 2010

The m1 scale has been defined (Chen and Atkinson, 2002) in the frequency domain, where the Fourier acceleration amplitude at 1 Hz is employed. The mhf and Mlp magnitude scales are determined accordingly with the high-frequency acceleration spectrum and the low-frequency displacement spectrum, respectively. This article deals with the similarity and correlations of these new magnitude scales with the popularly used moment magnitude (M) and the magnitude scales defined in the time domain, such as mb, MS, and ML, among others. The magnitudes m1, mhf, and Mlp are associated with intermediate-, high-, and low-frequency bands, respectively, estimated from spectra corrected for geometric and anelastic scattering effects. Comparisons between the magnitude scales demonstrate that m1 is a reliable indicator of earthquake size, which is not only well correlated with the local or regional magnitude but also is a good measure of the moment magnitude for at least small-to-moderate earthquakes.

Bindi D.,Helmholtz Center Potsdam | Bindi D.,Italian National Institute of Geophysics and Volcanology | Luzi L.,Italian National Institute of Geophysics and Volcanology | Parolai S.,Helmholtz Center Potsdam | And 3 more authors.
Bulletin of Earthquake Engineering | Year: 2011

In this work, we investigate the site amplification effects observed in the Norcia plain, Central Italy. Data from 30 selected local earthquakes (2 ≤ Ml ≤ 4.1) recorded by a temporary seismic network composed by 15 stations, are analyzed to determine the spatial variability of site effects. Both the Horizontal-to-Vertical spectral ratio and the Standard Spectral Ratio techniques are applied to estimate the site amplification effects. The results show that most of the sites in the valley are affected by strong amplifications (up to a factor of 20) in the frequency range 0.5-5 Hz. The value of the fundamental frequency of resonance is strictly dependent on the location within the basin and on the sediment thickness. Strong amplifications also affect the vertical components. The time-frequency analysis performed on a station located inside the basin shows the presence of a large spectral amplitudes after the S-wave phase, not observed on a station located on the bedrock, suggesting the presence of locally generated wave trains. Then, in agreement with earlier observations for other alluvial basins in Central Italy, 2D-3D effects play an important role in determining the site amplification effects in Norcia. © 2011 Springer Science+Business Media B.V.

Oth A.,European Center for Geodynamics and Seismology | Bindi D.,Helmholtz Center Potsdam | Parolai S.,Helmholtz Center Potsdam | di Giacomo D.,Helmholtz Center Potsdam | di Giacomo D.,International Seismological Center
Bulletin of the Seismological Society of America | Year: 2011

In this study we apply a nonparametric spectral inversion scheme to a data set of accelerograms recorded by the K-NET and KiK-net networks in Japan in order to derive attenuation characteristics, source spectra, and site response. For this purpose, we use a total of more than 67,000 S-wave records from 2178 earthquakes (MJMA 2.7-8) obtained at 1555 stations at the Earth's surface and more than 29,000 records from 1826 events recorded at 637 borehole stations at depths of 100 to 3000 m. Attenuation characteristics are investigated in five separate regions, showing that crustal Q depicts lower values in central compared to southern Japan, and a significant frequency dependence is observed in every region. The source spectra follow the ω2 model with higher stress drops for subcrustal earthquakes as compared with crustal ones. While strong amplification effects dominate the site contributions for the surface sensors, those for the borehole sensors are characterized by smaller variability. Nevertheless, consistent with observations from deconvolution of borehole/surface recording pairs, downgoing wave effects are visible in the site contributions for many borehole stations. Finally, the site amplification functions obtained at the surface are compared with surface-to-borehole (S/B) and horizontal-to-vertical (H/V) spectral ratios, showing that the S/B ratios generally provide better estimates of the horizontal amplification than the H/V ratios due to amplification of the vertical component of ground motion.

Bondar I.,International Seismological Center | Storchak D.,International Seismological Center
Geophysical Journal International | Year: 2011

The International Seismological Centre (ISC) is a non-governmental, non-profit organization with the primary mission of producing the definitive account of the Earth's seismicity. The ISC Bulletin covers some 50 yr (1960-2011) of seismicity. The recent years have seen a dramatic increase both in the number of reported events and especially in the number of reported phases, owing to the ever-increasing number of stations worldwide. Similar ray paths will produce correlated traveltime prediction errors due to unmodelled heterogeneities in the Earth, resulting in underestimated location uncertainties, and for unfavourable network geometries, location bias. Hence, the denser and more unbalanced the global seismic station coverage becomes, the less defensible is the assumption (that is the observations are independent), which is made by most location algorithms. To address this challenge we have developed a new location algorithm for the ISC that accounts for correlated error structure, and uses all IASPEI standard phases with a valid ak135 traveltime prediction to obtain more accurate event locations. In this paper we describe the new ISC locator, and present validation tests by relocating the ground truth events in the IASPEI Reference Event List, as well as by relocating the entire ISC Bulletin. We show that the new ISC location algorithm provides small, but consistent location improvements, considerable improvements in depth determination and significantly more accurate formal uncertainty estimates. We demonstrate that the new algorithm, through the use of later phases and testing for depth resolution, considerably clusters event locations more tightly, thus providing an improved view of the seismicity of the Earth. © 2011 The Authors Geophysical Journal International © 2011 RAS.

Di Giacomo D.,International Seismological Center | Storchak D.A.,International Seismological Center
Journal of Seismology | Year: 2016

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 mb and surface wave MS. 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. © 2015, Springer Science+Business Media Dordrecht.

Storchak D.A.,International Seismological Center | Di Giacomo D.,International Seismological Center | Engdahl E.R.,University of Colorado at Boulder | Harris J.,International Seismological Center | And 4 more authors.
Physics of the Earth and Planetary Interiors | Year: 2015

In this introductory article we give a general description of the ISC-GEM Global Instrumental Earthquake Catalogue (1900-2009). We also provide the background for four further articles that describe the effort in collecting and digitizing parametric earthquake bulletin data as well as the methodologies developed to compute homogeneous earthquake parameters. The result of the two and a half year project is a catalogue of approximately 20,000 large earthquakes covering 110. years with hypocentres and uncertainties computed using the same technique and velocity model. We show that the overall homogeneity of the main earthquake parameters in the catalogue was achieved despite changes in instrumentation and routine measurement practices concurrent with developments in instrumental seismology from almost a ground level to its current state.For each earthquake, MW magnitude values and uncertainties were computed either based on available estimates of seismic moment or using new empirical relationships between MW., MS and mb. Further important results of this project include the electronic availability of a considerable volume of seismic wave arrival time and amplitude measurements from early instrumental printed station bulletins. These newly recovered amplitude measurements provided a basis for computation of many previously unavailable MS magnitudes with uncertainties.In this article we describe why such a catalogue is required for a comprehensive assessment of global and regional seismic hazard. We also describe other potential uses of the catalogue in many other fields of Earth Sciences. We discuss the catalogue availability and lay out the plans of further development. © 2014 Elsevier B.V.

Oth A.,European Center for Geodynamics and Seismology | Bindi D.,Helmholtz Center Potsdam | Parolai S.,Helmholtz Center Potsdam | Di Giacomo D.,Helmholtz Center Potsdam | Di Giacomo D.,International Seismological Center
Geophysical Research Letters | Year: 2010

We investigate earthquake source characteristics and scaling properties using the results of a spectral inversion of more than 29,000 accelerometric borehole recordings from 1,826 earthquakes (MJMA 2.7-8) throughout Japan. We find that the calculated source spectra can be well characterized by the omega-square model and show on average self-similar scaling over the entire magnitude range, with median stress drops of 1.1 and 9.2 MPa for crustal and subcrustal events, respectively. The seismic energy-to-moment ratio, as theoretically expected if the omega-square model is valid, shows a strong dependency on stress drop only, which, in conjunction with data selection practice in some studies to cope with limited recording bandwidth, can explain the often observed apparent scale-dependence. Our observations suggest that there is no significant deviation from similarity of the energy radiation in the investigated magnitude range and that the observed scatter is mainly related to the scatter in stress drop. © 2010 by the American Geophysical Union.

Grant
Agency: NSF | Branch: Continuing grant | Program: | Phase: INSTRUMENTATION & FACILITIES | Award Amount: 750.78K | Year: 2014

This grant allows for renewed partial support of operations of the International Seismological Centre (ISC). The ISC is internationally supported and the requested budget is based on the relative GDPs of sponsor countries with funding from the U.S. near 20% of the estimated operational costs over this period. Support provides for continued production of the ISC Bulletin - the definitive global summary of earthquake hypocentres, magnitudes and source mechanisms, as well as station arrival times, amplitudes and other measurements with links to original waveforms where available. The international supported and non-governmental affiliation of the ISC allows the Centre to collect and freely distribute data from otherwise unavailable sources of global seismic recordings. The ISC Bulletin supports the global seismology community for fundamental research on Earth structure, earthquake physics and earthquake hazards mitigation. The Bulletin also aids in monitoring of the Comprehensive Test Ban Treaty.

ISC data products, in particular the global catalog of observed arrival times, amplitudes, and associated meta data, are a starting point for fundamental studies of Earth structure and earthquake source mechanisms. Support under this grant will allow for continued development and refinement of seismic event parameters that are published in the ISC bulletin and available on line as well as new efforts to extend the catalog back in time to the 1900 (pre-digital seismic recordings) and to a lower magnitude threshold. The improved seismic event records will allow for improved understanding of historical global seismicity and lead to better models of Earths interior structure, the later critical to identifying seismic event source mechanisms, magnitudes and locations that aid in comprehensive nuclear test ban treaty monitoring. ISC products are critical to maintaining definitive accurate seismic event provenance over decadal time scales and contribute to improved earthquake resistant civil engineering globally.

Specific tasks to be supported include: 1) ongoing collection, automatic merging and association of reported bulletin data from networks and data centers around the world, including National Earthquake Information Center (NEIC), USArray, Comprehensive Test Ban Treaty Office (CTBTO), Japanese Meteorological Agency (JMA) etc.; 2) manual review of hypocentres, phase readings, and related data for events simultaneously reported by several networks approximately of magnitude 3.5 and above; 3) distribution of the ISC Bulletin by means of the web-search, ftp, CD-ROMs and the printed ISC Bulletin Summary; 4) maintenance and re-development of the International Seismograph Station Registry jointly with the National Earthquake Information Center operated by the US Geological Survey and in coordination with the Federation of Digital Seismograph Networks (FDSN); 5) maintenance and update of the International Association of Seismology and Physics of the Earths Interior (IASPEI) Collection of Reference Events (GT0-5); 6) partial support for extension of the ISC-GEM Global Instrumental Earthquake Catalogue -- the most homogeneous global long-term catalog used for global and regional seismic hazard assessment; and 7) maintenance and extension of the ISC Event Bibliography, which allows for rapid literature searches pertaining to significant global seismic events.

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