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Goran Ekstrom - One of the best experts on this subject based on the ideXlab platform.
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calibration of the hglp seismograph network and centroid moment tensor analysis of significant earthquakes of 1976
Physics of the Earth and Planetary Interiors, 1997Co-Authors: Goran Ekstrom, M NettlesAbstract:Abstract A methodology is developed for determining accurate instrument response functions for Seismographs of the High-Gain Long-Period (HGLP) Network. Recordings of daily transient calibration pulses provide a detailed history of the time-varying responses of the HGLP stations. When the instrument displacement transfer function is available, knowledge of the seismometer mass, calibration coil constant, and calibration current allows for the prediction of the shape and amplitude of the calibration signal by simple integration of the transfer function. In theory the inverse of this statement is also true, but in practice noise in the recordings contaminates the instrument response function recovered through direct differentiation of the calibration pulse. The unknown transfer function of the seismograph system is, instead, first described by the product of the nominal responses of its mechanical and electromagnetic components. Specific values of the characteristic parameters for each seismograph component are subsequently determined by iterative least-squares minimization of the misfit between observed and model transient calibration pulses. By application of this method to daily calibration pulses recorded on the ten stations of the HGLP network, refined instrument response functions for 1976 and part of 1975 are determined. The results agree well with single frequency amplitude calibration data recovered from station maintenance records, and produce synthetic waveforms which are consistent with data from other well-calibrated stations. We use the recalibrated HGLP data together with long-period data from early International Deployment of Accelerometers (IDA) and Seismic Research Observatory (SRO) digital stations to determine 108 centroid-moment tensor (CMT) solutions for moderate and large earthquakes of 1976. The new CMT results for several major earthquakes, including the Tangshan, Guatemala, and Friuli events, are compared with those of previous studies.
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instrument responses of digital Seismographs at borovoye kazakhstan by inversion of transient calibration pulses
Bulletin of the Seismological Society of America, 1996Co-Authors: Wonyoung Kim, Goran EkstromAbstract:Abstract A method is developed to determine the response of digital Seismographs from transient calibration pulses. Based on linear system theory, the digital seismograph is represented by a set of first- and higher-order linear filters characterized by their cutoff frequencies and damping coefficients. The transient calibration pulse is parameterized by a set of instrument constants, and the problem is linearized for small perturbations of the constants with respect to their nominal values. The observed calibration pulse shape is matched in the time domain using an iterative linearized inverse technique. The method is used to derive complete instrument responses for digital Seismographs operating at the Borovoye Observatory (BRVK) in Kazakhstan, for which previously only the amplitude responses have been determined. To test this method, we apply it to calibration pulses from a modern digital seismograph system at Kislovodsk (KIV) in northern Caucasus, Russia, and obtain good agreement between known and derived instrument constants. The results of the calibration pulse shape inversion for these Seismographs indicate that the method is efficient and that the results are reliable even when microseismic noise is present in the recorded transient calibration pulse. The derived parameters make possible improved quantitative waveform analysis of digital seismograms recorded at BRVK.
Yasushi Ishihara - One of the best experts on this subject based on the ideXlab platform.
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verification of horizontal to vertical spectral ratio technique for estimation of site response using borehole Seismographs
Bulletin of the Seismological Society of America, 2001Co-Authors: Seiji Tsuboi, Masanori Saito, Yasushi IshiharaAbstract:The City of Yokohama has established a high-density strong-motion seismograph network in 1997 to enable rapid evaluation of seismic hazard in case of disastrous earthquakes. It consists of 150 surface strong-motion Seismographs and nine borehole strong-motion Seismographs within the city area, which is approximately 20 km × 30 km wide. We use seismograms recorded by the borehole Seismographs of the network from seven earthquakes that occurred around Yokohama. We calculate the S -wave spectral ratio between the surface seismograph and the borehole seismograph and compare it with a synthetic spectral ratio calculated from a velocity profile of the borehole. The agreement of observed and synthetic spectral ratios is excellent, which shows that we may use these borehole Seismographs to test various techniques for estimation of the site amplification. We then apply the horizontal-to-vertical (H/V) spectral-ratio technique for seismograms recorded at the surface and compare them with these spectral ratios. The results show that the H/V ratio technique gives a good estimate of the surface amplification for frequency range between about 1 and 4 Hz, if the near-surface velocity structure is relatively simple and if the signal-to-noise ratio of seismograms recorded at the surface is adequate.
M Nettles - One of the best experts on this subject based on the ideXlab platform.
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calibration of the hglp seismograph network and centroid moment tensor analysis of significant earthquakes of 1976
Physics of the Earth and Planetary Interiors, 1997Co-Authors: Goran Ekstrom, M NettlesAbstract:Abstract A methodology is developed for determining accurate instrument response functions for Seismographs of the High-Gain Long-Period (HGLP) Network. Recordings of daily transient calibration pulses provide a detailed history of the time-varying responses of the HGLP stations. When the instrument displacement transfer function is available, knowledge of the seismometer mass, calibration coil constant, and calibration current allows for the prediction of the shape and amplitude of the calibration signal by simple integration of the transfer function. In theory the inverse of this statement is also true, but in practice noise in the recordings contaminates the instrument response function recovered through direct differentiation of the calibration pulse. The unknown transfer function of the seismograph system is, instead, first described by the product of the nominal responses of its mechanical and electromagnetic components. Specific values of the characteristic parameters for each seismograph component are subsequently determined by iterative least-squares minimization of the misfit between observed and model transient calibration pulses. By application of this method to daily calibration pulses recorded on the ten stations of the HGLP network, refined instrument response functions for 1976 and part of 1975 are determined. The results agree well with single frequency amplitude calibration data recovered from station maintenance records, and produce synthetic waveforms which are consistent with data from other well-calibrated stations. We use the recalibrated HGLP data together with long-period data from early International Deployment of Accelerometers (IDA) and Seismic Research Observatory (SRO) digital stations to determine 108 centroid-moment tensor (CMT) solutions for moderate and large earthquakes of 1976. The new CMT results for several major earthquakes, including the Tangshan, Guatemala, and Friuli events, are compared with those of previous studies.
Andrzej Kijko - One of the best experts on this subject based on the ideXlab platform.
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The South African National Seismograph Network
Seismological Research Letters, 2008Co-Authors: Ian Saunders, Martin B. C. Brandt, Johan Steyn, Dale Roblin, Andrzej KijkoAbstract:Seismic monitoring in South Africa prior to 1970 was through sporadic deployment of Seismographs by various institutions. The first was a Wiechert seismograph installed at Union Observatory in Johannesburg in 1910 to monitor mining-related earthquakes (Gane 1939). Table 1, after Wright and Fernandez (2003), shows in brief the monitoring status in South Africa for the period 1910 to 1981. Following the devastating magnitude 6.3 earthquake in Western Cape Province during September 1969, the Geological Survey (now the Council for Geoscience) deployed seven Seismographs in South Africa and heralded the start of organized seismic monitoring in the country and the establishment of the South African National Seismograph Network (SANSN). The network expanded during the following years to a maximum of 27 stations in 1997. The SANSN remained analog until 1991 when a number of digital Seismographs were installed either in parallel with existing analog equipment or as new stations. Data communication with digital stations was facilitated through dial-up landlines (Fernandez et al. 1991). With the advent of Global System for Mobile Communications (GSM) in South Africa, a limited number of stations were equipped with dial-up cellular modems. The SANSN was modernized during 2003 through a government grant that facilitated the purchase and installation of three-component extended short-period (30 s) and broadband (100 s) sensors. This marked a turning point for the SANSN because prior to the upgrade the network largely consisted of vertical-component short-period sensors. View this table: TABLE 1 Seismic Instrumentation Deployed in South Africa During the Period 1910 to 1981 (after Wright and Fernandez 2003 ) The lessons learned from the delay in waveform data transfer after the magnitude 5.3 earthquake in Stilfontein (Klerksdorp gold mines) on 9 March 2005 (see figure 1 for damage to a building in the central business district of Stilfontein and figure 2 for a seismogram of the …
Seth R. Lemke - One of the best experts on this subject based on the ideXlab platform.
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Earthquake Seismographs for Volunteers to Operate in K-12 Classrooms
Seismological Research Letters, 2003Co-Authors: Wayne D. Pennington, Sean Wagner, Shannon E. Bair, Seth R. LemkeAbstract:We have completed development of a seismograph system that is easy to operate and relatively inexpensive to purchase, one that is intended to be used for teaching Earth sciences to students K-12, using earthquakes recorded in the classroom from around the world. This seismograph is computer-based and self-contained, requiring no hook-ups to the Internet or to advanced timing devices, and can be operated in a classroom for two or three months at a time. Typically, this allows the recording of two to three very large earthquakes somewhere in the world that are used in the related activities. Our intention is to assist teachers and volunteers with bringing Earth science into the classroom by making it easier to obtain and operate Seismographs. Several programs in existence today encourage schools to maintain and operate earthquake Seismographs of research-level quality, such as MichSeis and its affiliates, through the University of Michigan (http://www.geo.Lsa.umich.edu/MichSeis/), and PEPP, the Princeton Earth Physics Project, through Princeton University (http://lasker.princeton.edu/). These are excellent programs, and we encourage schools and teachers to become involved with them. On the other hand, the continual operation and maintenance of a research-quality earthquake seismograph is a large obligation for most K-12 schools to consider. A highly dedicated teacher (or friend) must be prepared to devote considerable time to learning the system, maintaining the records, and communicating results back to a central reporting station. Most schools would like to be involved with a demonstration for some time but then not be saddled with a continuing commitment beyond the initial enthusiasm. The focus of our efforts was to create a turnkey system that is easy to operate and will maximize use by volunteers and teachers. With support from the SEG Foundation, we developed a user-friendly seismograph station that can be operated by volunteers with little or no …
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Earthquake Seismographs For Volunteers to Operate In K-12 Classrooms
SEG Technical Program Expanded Abstracts 2000, 2000Co-Authors: Wayne D. Pennington, Shannon E. Bair, Seth R. LemkeAbstract:© 2000 Society of Exploration Geophysicists. We have completed development of a seismograph system that is easy to operate and relatively inexpensive to purchase, one that is intended to be used for teaching earth sciences to students of all ages, by recording earthquakes from around the world, right in their classroom. This seismograph is computer-based and self-contained, requiring no hook-ups to the internet or to advanced timing devices, and can be operated in a classroom for two or three months at a time, allowing the recording of, typically, a few very large earthquakes somewhere in the world. It is our intention to make it easy for volunteers to obtain and operate Seismographs in their local schools, and to assist teachers in bringing earth science to the classroom in a very meaningful way
