WWSSN Research Articles

The Repeating Major Earthquakes in the Mexican Subduction Zone Along Oaxaca: Implications for Future Events

Abstract The subduction zone along Oaxaca, Mexico, has experienced multiple Mw ≥ 7 earthquakes that ruptured in close proximity several decades apart in at least three locations along the coast. Similarity of waveform recordings from a few long-period seismic stations at teleseismic distances has provided evidence for up to three repeated failures of the same slip patches, or persistent asperities, in the region. The evidence from prior single-station comparisons is bolstered by considering azimuthally distributed sets of body-wave recording pairs for the 1968 and 2018 Pinotepa Nacional (western Oaxaca), and 1965 and 2020 La Crucecita (eastern Oaxaca) earthquakes, as viewed in the long-period World-Wide Standardized Seismograph Network instrument passband (>5 s period). Drawing on detailed slip inversions for the most recent events and observations of their relationships with regional slow-slip events, we note features to be alert for in central Oaxaca where prior repeating events in 1928 and 1978 occurred and there is potential for a similar future event.

Classifying Worldwide Standardized Seismograph Network Records Using a Simple Convolution Neural Network

Abstract The U.S. Geological Survey (USGS) maintains an archive of 189,180 digitized scans of analog seismic records from the World-Wide Standardized Seismograph Network (WWSSN). Although these scans have been made public, the archive is too large to manually review, and few researchers have utilized large numbers of these records. To facilitate further research using this historical dataset, we develop a simple convolutional neural network (CNN) that rapidly (∼4.75 s/film chip) classifies scanned film chip images (called “chips,” because they are individually cut segments of 70 mm film) into four categories of “interestingness” to earthquake seismologists based on the presence of earthquakes and other seismic signals in the record: “no interest,” “little interest,” “interest,” and “high interest.” The CNN, dubbed “Seismic Analog Record Network” (SARNet), can identify four types of seismic traces (“no events,” “minor events,” “major events,” and “errors”) in 200 × 200 pixel subcrops with an accuracy of 92% using a confidence threshold of 85%. SARNet then converts 100 random subcrops from each film chip into the overall classification of interestingness. In this task, SARNet performed as well as expert human classifiers in determining the film chip’s overall interest grade. Applying SARNet to 34,000 film chips in the WWSSN archive found that 21% of the images were of “high interest” and had an “indeterminate” rate of only 4%. Thus, the need for the manual review of images was reduced by 79%. Sorting of film chips derived from SARNet will expedite further exploration of the archive of digitized analog seismic records stored at the USGS.

100 Years of Paper Seismograms from Denmark and Greenland, 1907–2008

Abstract The paper seismograms from 100 years of observations in Denmark and Greenland has since October 2021 been made available through the Danish National Archives. Five case stories illustrate the quality and variation of the seismograms, and the historical context of operation of the stations. (1) The earliest recorded earthquake in the archive is recorded at GDH station in Greenland, where the 1907 Mw 7.2 earthquake in Tajikistan is recorded on smoked paper. (2) The first Danish earthquake is a local event close to Copenhagen in 1930. (3) We have illustrated the 50 megaton nuclear explosion in Novaya Zemlya in 1961—the largest nuclear test explosion ever. (4) The M 9.2 earthquake in Alaska in 1964 recorded on several instruments at COP. (5) A local earthquake in northeast Greenland recorded both on paper on World-Wide Standard Seismographic Network instruments and digitally on a modern broadband instrument.

Analog Seismogram Archives at the Earthquake Research Institute, the University of Tokyo

Abstract The Earthquake Research Institute (ERI) of the University of Tokyo maintains archives of analog seismograms and mareograms. The main collection is ∼236,000 Japanese historical seismograms recorded at the University of Tokyo (at various buildings and using various instruments around Hongo [Tokyo] with a total of 189,000 records from 1881 to 1993), at the Tsukuba observatory (∼11,000 records from 1921 to 1986), and at the Wakayama seismological network (∼12,650 records from 1928 to 1968). Seismograms recorded by temporal stations at various locations in Japan for several years, typically following large earthquakes, are also included. Different types of instruments were used to record the data. The oldest record from a large earthquake is from the 1891 Nobi earthquake recorded at Hongo on a circular seismogram using an Ewing-type seismograph. Teleseismic seismograms include those from the 1899 Alaska earthquake at Hongo on an Omori-type seismograph. Imamura-type and Omori-type tremometers and strong-motion seismographs had also been used for a long time. While these seismograms were microfilmed by the 1990s, the original smoked paper records have also been archived. Foreign seismogram collections include those from earthquakes in Taiwan between 1904 and 1917 recorded in both Japan and Taiwan and those from the Canadian Seismograph Network between 1981 and 1989. For the Worldwide Standardized Seismograph Network stations, almost all (∼5,000,000) microfilm records at 167 stations from 1963 to 1988 are archived. High-resolution image scanning of analog daily seismograms at the Wakayama microearthquake network is currently being performed, and the scans are provided using Leaflet software so that the users can easily access and enlarge parts of seismograms. The tsunami waveform archive contains ∼3100 records on Japanese tide gauges from large earthquakes between 1911 and 1996. The available data, with dates and types of instruments, can be searched from the database through the website of the ERI.

Investigation of the stable and unstable states of seismographs using poles and zeros pattern

In this study, a simple Simulink model was designed and presented which can describe the overall operation of seismograph based on the desired input and output response.By converting Laplace to seismograph equations and by defining Numerator and Denominator fractions to Num. and Den. (Numerator and Denominator) transfer WWSSN (World-Wide Standard Seismographic Network) functions, the changeability of pole-zero was taken into consideration which indicates the stability and instability of the system layout with respect to pole - zero layout. In fact, the poles and zeros are placed in the seismograph response based on frequency, amplitude and phase (FAP) and are analyzed well. Through this method can also be used to study seismograph transfer function to predict the seismograph output in environments with different seismic noise and to select the most appropriate value for the parameters controlling the output of the device.

SKATE: A Web‐Based Seismogram Digitization Tool

Research Article| August 08, 2018 SKATE: A Web‐Based Seismogram Digitization Tool Andrew H. Bartlett; Andrew H. Bartlett aRetriever Technology, 1600 Lena Street, STE D1, Santa Fe, New Mexico 87505 U.S.A. Search for other works by this author on: GSW Google Scholar Benjamin A. Lichtner; Benjamin A. Lichtner aRetriever Technology, 1600 Lena Street, STE D1, Santa Fe, New Mexico 87505 U.S.A. Search for other works by this author on: GSW Google Scholar Marius Nita; Marius Nita aRetriever Technology, 1600 Lena Street, STE D1, Santa Fe, New Mexico 87505 U.S.A. Search for other works by this author on: GSW Google Scholar Benamy Yashar; Benamy Yashar aRetriever Technology, 1600 Lena Street, STE D1, Santa Fe, New Mexico 87505 U.S.A. Search for other works by this author on: GSW Google Scholar Lowell E. Bartlett Lowell E. Bartlett aRetriever Technology, 1600 Lena Street, STE D1, Santa Fe, New Mexico 87505 U.S.A. Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2018) 89 (5): 1886–1893. https://doi.org/10.1785/0220180006 Article history first online: 08 Aug 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation Andrew H. Bartlett, Benjamin A. Lichtner, Marius Nita, Benamy Yashar, Lowell E. Bartlett; SKATE: A Web‐Based Seismogram Digitization Tool. Seismological Research Letters 2018;; 89 (5): 1886–1893. doi: https://doi.org/10.1785/0220180006 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietySeismological Research Letters Search Advanced Search ABSTRACT Vast stores of paper‐ and film‐based seismograms require novel solutions to extract their unique seismological data. We created a prototype software tool called SKATE (Software Kit for Automatic Trace Extraction) that is designed for high‐speed, low‐cost digitization of these archives. SKATE is a web‐based program that requires a user only to navigate to a website (see Data and Resources) to begin digitizing seismogram images. The software is free, is server based, requires no software downloads, is open source, and has digitized up to the point of editing more than 30,000 World‐Wide Standard Seismographic Network (WWSSN) images. It is based on a set of image‐processing algorithms that identify real seismogram features while rejecting spurious noise and which attempts to assign these features to their proper place in a time series. Users can edit the results and download the data for further processing. The code is publicly available and is readily modifiable by qualified researchers. You do not currently have access to this article.

An Investigation of MbLg Versus Mw for Eastern North America

Research Article| May 01, 2014 An Investigation of MbLg Versus Mw for Eastern North America Christopher Rigsby; Christopher Rigsby aDepartment of Earth and Atmospheric Sciences, Saint Louis University, 3642 Lindell Boulevard, St. Louis, Missouri 63108 U.S.A.rbh@eas.slu.edu Search for other works by this author on: GSW Google Scholar Robert B. Herrmann; Robert B. Herrmann aDepartment of Earth and Atmospheric Sciences, Saint Louis University, 3642 Lindell Boulevard, St. Louis, Missouri 63108 U.S.A.rbh@eas.slu.edu Search for other works by this author on: GSW Google Scholar Harley Benz Harley Benz bNational Earthquake Information Center, U.S. Geological Survey, Denver Federal Center, Box 25046, MS 966, Denver, Colorado 80225 U.S.A.benz@usgs.gov Search for other works by this author on: GSW Google Scholar Author and Article Information Christopher Rigsby aDepartment of Earth and Atmospheric Sciences, Saint Louis University, 3642 Lindell Boulevard, St. Louis, Missouri 63108 U.S.A.rbh@eas.slu.edu Robert B. Herrmann aDepartment of Earth and Atmospheric Sciences, Saint Louis University, 3642 Lindell Boulevard, St. Louis, Missouri 63108 U.S.A.rbh@eas.slu.edu Harley Benz bNational Earthquake Information Center, U.S. Geological Survey, Denver Federal Center, Box 25046, MS 966, Denver, Colorado 80225 U.S.A.benz@usgs.gov Publisher: Seismological Society of America First Online: 14 Jul 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 2014 by the Seismological Society of America Seismological Research Letters (2014) 85 (3): 625–630. https://doi.org/10.1785/0220130138 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Christopher Rigsby, Robert B. Herrmann, Harley Benz; An Investigation of MbLg Versus Mw for Eastern North America. Seismological Research Letters 2014;; 85 (3): 625–630. doi: https://doi.org/10.1785/0220130138 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search Since the introduction of the concept of magnitude to seismology by Richter (1935), many different magnitude scales have been proposed. The United States Geological Survey National Earthquake Information Center (NEIC) routinely uses many of these, including moment magnitude, Mw (Hanks and Kanamori, 1979); energy magnitude, Me (Choy and Boatwright, 1995); surface‐wave magnitude, Ms (International Association of Seismology and Physics of the Earth’s Interior, IASPEI); short‐period teleseismic P‐wave magnitude, mb (Gutenberg and Richter, 1956); local magnitude, ML (Richter, 1935; Hutton and Boore, 1987); surface‐wave magnitude... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The seismicity in Kenya (East Africa) for the period 1906–2010: A review

Kenya has had a seismic station since 1963 as part of the World Wide Standardized Seismograph Network (WWSSN). In 1990, the University of Nairobi in collaboration with GeoForschungsZentrum (GFZ) started to build up a local seismological network, the Kenya National Seismic Network (KNSN), which operated for about ten years between 1993–2002. This, however, experienced a myriad of problems ranging from equipment breakdown, vandalism and lack of spares. Kenya is seismically active since the Kenya rift valley traverses through the country from north to south bisecting the country into eastern and western regions. In the central part, the Kenya rift branches to form the NW-SE trending Kavirondo (Nyanza) rift. The Kenya rift valley and the Kavirondo (Nyanza) rift are the most seismically active where earthquakes of local magnitude (Ml) in the order of ⩽2.0–5.0 occur. Furthermore, historical records show that earthquakes of magnitudes of the order of Ml⩾6.0 have occurred in Kenya. Such large magnitude earthquakes include the January 6, 1928 Subukia earthquake (Ml 7.1) and an aftershock (Ml 6.2) four days later, as well as the 1913 Turkana region earthquake (Ml 6.2). Since early 1970’s, numerous seismic investigations have been undertaken in Kenya in order to understand the formation and structure of the Kenyan part of the East African rift valley. Earthquake data from these studies is, however, rather disorganized and individual datasets, including that acquired during the period 1993–2002, cannot furnish us with comprehensive information on the seismicity of Kenya for the past ∼100years. The purpose of this paper is, therefore, to review the seismicity in Kenya for the period 1906–2010 by utilizing data and results from different sources. The general seismicity of Kenya has been evaluated using historical data, data recorded by local seismic networks, the United States Geological Survey catalogue as well as earthquake data from the numerous seismic investigations by different individuals and research groups. On the basis of earthquake data from these sources, the entire N–S trending Kenya rift valley and the NW-SE trending Nyanza (Kavirondo) rift are characterized by a high rate of seismicity, and the USGS network has been effective in detecting local M>3.0 earthquakes. A peculiar trend is exhibited by earthquakes of Ml⩾5.1 in that these occur along the N-S and NW-SE trending Kenya rift valley and the Kavirondo (Nyanza) rift zone respectively. Earthquake data from the various sources for the period 1906–2010 is complete for Ml⩾4.4 earthquakes with a b-value of 0.79 which is characteristic of tectonic active regions like rifts. There is need to revive and extend the KNSN for a greater coverage and effective seismic monitoring in Kenya.

The Argentinean National Network of Seismic and Strong-Motion Stations

The history of seismic studies in Argentina dates back to the first decades of the last century and is based on historical material and archeological evidence. The first institution in the country devoted to geophysical aspects (mainly seismology) was the Astronomic Observatory of La Plata, created in 1882. But it was not until 1906 that this institution included seismic observations by installing the first seismological equipment, consisting of a three‐component Vicentini seismograph, in 1907. Between 1913 and 1925 two more mechanical seismographs were installed by the Astronomic Observatory of La Plata. This institution started publishing its first annual bulletin in 1922. In 1951, two electromagnetic‐type seismographs were installed at the Observatory, which increased significantly the registration of seismic events. One of the stations of this Observatory became part of the World Wide Standardized Seismograph Network (WWSN) in 1962. In January 1944 a large earthquake ( M w 7.0; Alvarado and Beck, 2006) almost completely destroyed the city of San Juan, the capital of San Juan province, located in the west‐central part of Argentina, killing at least 5000 people. This earthquake was the trigger for seismological research and seismic observations in Argentina, especially in San Juan province. Following this earthquake in 1944, the Federal Government created the Consejo Nacional de Construcciones Antisismicas y de Reconstruccion de San Juan (CONCAR), an institution devoted to develop a new building code and to plan and carry out the reconstruction process of San Juan city. On 8 May 1972, the CONCAR was transformed into the National Institute for Seismic Prevention (INPRES). INPRES is a federal agency of the Argentine government depending on the Secretary of Public Services and is situated in the city of San Juan. Its main objective is to carry out the national policy for seismic prevention, operate the national network of seismic stations …

Great Earthquakes and Global Seismic Networks

Seismologists often jest that “the best way to stop earthquakes is to deploy seismic stations.” The laborious effort to install seismometers to record signals from earthquakes or to pursue targeted investigations of Earth's structure is sometimes confounded by the vagaries of earthquake occurrence, which is decidedly nonuniform in space and time. Of course, this often proves to be more of an anxiety than a reality, and most efforts, especially those employing multiyear installations, succeed in gathering valuable seismic data. One of the most gratifying examples of success is provided by the deployment of the Incorporated Research Institutions for Seismology–National Science Foundation–U.S. Geological Survey (IRIS-NSF-USGS) Global Seismographic Network (GSN) in parallel with numerous international deployments of broadband seismometers in the Federation of Digital Seismic Networks (FDSN). Between about 1982 and 2004, global installations of high-quality broadband digital seismometers proliferated, replacing the obsolete analog systems of the World-Wide Standardized Seismograph Network and upgrading sparse institutional observatories and first-generation digital networks. While deployments of important additional stations continue, by 2004 the GSN had achieved its basic design goals: openly available continuous broadband data from roughly 130 stations providing real-time global coverage and large dynamic range (Butler et al. 2004). Then the 26 December 2004 great Sumatra-Andaman earthquake ( Mw 9.2) occurred—the first event to exceed magnitude 9 since the 1964 Alaska earthquake. The GSN and FDSN provided unprecedented global seismic recordings for this event and enabled more detailed seismological investigation than was possible for any prior event of such size ( e.g. , Lay et al. 2005; Bilek et al. 2007). Those same globally distributed seismic stations have gathered data from a substantial number of great earthquakes; from 2001 to 2010, there have been 18 events with MS ≥ 8 and 13 events with Mw ≥ 8, whereas over the previous …

Preface to the Special Issue on “Arrays and Array Methods in Global Seismology”

The increased availability and fidelity of broadband seismic instruments have played a key role in bridging the gap between exploration and global seismic applications. Long gone are the days when global structure mapping and source characterization/monitoring relied on the manual digitization of WWSSN (World-Wide Standard Seismographic Network) analogue records or hours in front of microfiche machines. Even the GSN (Global Seismographic Network), a milestone of the digital era, now pales in comparison with the scope and density of regional seismic arrays that dominate the global data stream. Today, the nominal resolution estimated from the ratio between wavelength (approximately tens to hundreds of kilometers) and target dimension (often of continental scale) in properly designed global experiments could rival the typical resolution of a controlled source seismic survey. Vastly improved data coverage, highlighted by multi-disciplinary initiatives such as the USArray project, has overcome many conceptual (as well as practical) barriers between exploration and global seismic applications. A direct consequence is that the ‘‘global community’’ can now take full advantage of important array methods that are predicated upon superior data density and distribution. In fact, it could legitimately be argued that exploration seismology is fast becoming a realistic, scaled-down model for global seismic surveys. This Special Issue reviews the assumptions, algorithms and prospects of several important methodologies in today’s global and regional seismic surveys. A key objective is to highlight developments and novel applications that improve our ability to determine seismic structures across all spatial scales. We mainly emphasize those methodologies and applications that are relevant to structure imaging (note: source characterization may be detailed in a future Special Issue). Apart from the obvious scale differences between exploration (\20 km) and global (typically [ several 100 km) problems, we demonstrate that key objectives such as signal isolation, correlation, reconstruction and noise reduction

Determining earthquake epicentre from a single 3-component seismological station

An attempt has been made in this study to determine the epicentres by trigonometrical method from a single station using the three components of the ground's motion recorded by the Benioff Short Period Seismograph of the World Wide Standardized Seismograph Network (WWSSN) at Central Seismological Observatory (C.S.O.), Shillong. The trigonometrical method is based on the angle of bearing obtained from the ratio of the amplitudes of waves recorded on the horizontal components of the WWSSN seismograms. A comparison of recorded epicentres from the I.M.D. Seismological Network of Seismo, New Delhi with that of a single station i.e., C.S.O., Shillong has been made to estimate the accuracy of the method. The characteristics of the epicentral variations obtained from the Seismological Network of Seismo, New Delhi with that of C.S.O., Shillong are relatively small for local earthquakes compared to regional earthquakes with C.S.O., Shillong as the reference station. The characteristics of the epicentral variations particularly in the Shillong plateau are observed to be minimum. Strong correlations of epicentres are observed for both local as well as regional earthquake events.

The New IASPEI Standard Broadband Magnitude mB

Research Article| September 01, 2008 The New IASPEI Standard Broadband Magnitude mB Peter Bormann; Peter Bormann Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences Telegrafenberg 14473 Potsdam, Germany pb65@gmx.net (P.B.) saul@gfz-potsdam.de (J.S.) Search for other works by this author on: GSW Google Scholar Joachim Saul Joachim Saul Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences Telegrafenberg 14473 Potsdam, Germany pb65@gmx.net (P.B.) saul@gfz-potsdam.de (J.S.) Search for other works by this author on: GSW Google Scholar Author and Article Information Peter Bormann Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences Telegrafenberg 14473 Potsdam, Germany pb65@gmx.net (P.B.) saul@gfz-potsdam.de (J.S.) Joachim Saul Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences Telegrafenberg 14473 Potsdam, Germany pb65@gmx.net (P.B.) saul@gfz-potsdam.de (J.S.) Publisher: Seismological Society of America First Online: 09 Mar 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 2008 by the Seismological Society of America Seismological Research Letters (2008) 79 (5): 698–705. https://doi.org/10.1785/gssrl.79.5.698 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Peter Bormann, Joachim Saul; The New IASPEI Standard Broadband Magnitude mB. Seismological Research Letters 2008;; 79 (5): 698–705. doi: https://doi.org/10.1785/gssrl.79.5.698 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search Ten years after the development of a local magnitude scale, ML, by Richter (1935), Gutenberg (1945a, 1945b, 1945c) proposed to extend the magnitude concept to measurements of maximum amplitudes of body and surface waves at teleseismic distances. For the first time this made possible comparable estimates of earthquake size on a global scale (Gutenberg and Richter 1949, 1954). In addition, body waves allow magnitude measurements for earthquakes at all depths. Teleseismic magnitudes were originally determined for earthquakes with magnitudes mostly around 6 and larger on intermediate- to long-period displacement-proportional records... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Understanding the Differences between Three Teleseismic mb Scales

We investigate differences between three body-wave magnitude ( m b ) scales for 2009 earthquakes from 1996 to 1999 listed in the Preliminary Determination of Epicenter (pde) bulletin having m b between 5.0 and 5.5 and that also have moment tensor solutions available from the Harvard Centroid Moment Tensor (cmt) catalog. A total of 31,280 broadband seismograms are analyzed, for an average of 15 stations per event. Both the pde and Reviewed Event Bulletin (reb) procedures for determining an automated m b are reproduced, thereby eliminating any discrepancies that result from using different networks of stations. We compare the reproduced pde and reb magnitudes to another magnitude measurement, m b ( P ), that is based on the Worldwide Standard Seismographic Network (wwssn) short-period instrument. We find that differences between m b ( P ), m b (pde), and m b (reb) arise from four factors: response function, length of time window, and corrections for event depth and epicentral distance. Reproduced m b (pde) and m b ( P ) are strongly correlated, and we expect that magnitudes assigned from wwssn short-period instruments during the 1970s and 1980s are consistent with those assigned by the automated procedure used since 1991 by the U.S. Geological Survey (usgs), providing stability in m b measurements over several decades. The difference between m b (reb) and m b ( P ) is much greater because of the significantly shorter reb window length of 5.5 sec and the high-frequency passband of the reb displacement response. Online Material: Filter parameters and color versions of Figures 8 and 9.

The global seismographic network surpasses its design goal

This year, the Global Seismographic Network (GSN) surpassed its 128‐station design goal for uniform worldwide coverage of the Earth. A total of 136 GSN stations are now sited from the South Pole to Siberia, and from the Amazon Basin to the sea floor of the northeast Pacific Ocean—in cooperation with over 100 host organizations and seismic networks in 59 countries worldwide (Figure 1).Established in 1986 by the Incorporated Research Institutions for Seismology (IRIS) to replace the obsolete, analog Worldwide Standardized Seismograph Network (WWSSN),the GSN continues a tradition in global seismology that dates back more than a century to the network of Milne seismographs that initially spanned the globe. The GSN is a permanent network of state‐of‐the‐art seismological and geophysical sensors connected by available telecommunications to serve as a multi‐use scientific facility and societal resource for scientific research, environmental monitoring, and education for our national and international community.

Geophysics in the public service

Editor's note: Historical Perspective is a new feature to accommodate unsolicited articles that deal with historical records and personal perspectives of early geophysics. These invaluable documents are usually written in styles of their own that would often require extensive editing, reorganization, and/or fact verification to suit TLE standards—a process which could, in turn, rob them of their patina and even historical value. To differentiate them from Profiles, Mentoring, and other regular TLE human interest articles, and acknowledge their unique status as historical documents is the reason the Editorial Board has created this new feature. Here, these unsolicited and sometimes unorthodox contributions can be published with only the most essential of microedits and abridgements. Since its founding during 1930, the Society of Exploration Geophysicists (SEG) has conferred Honorary Memberships (its second highest award) on 135 recipients. Only two have gone to Washington, D.C., bureaucrats. The first of these was given to Vincent McKelvey, a minerals specialist and past director of the U.S. Geological Survey (1971–78). The second was awarded in 1981 to the author, a jack-of-all-trades within federal earth science for nearly four decades (1943–1979). Should you have called me a bureaucrat to my face, however, I would have quickly rejoined, “No! I was just a public servant!” By a combination of good fortune and serendipity, I became a student of or a collaborator with some of the United States's greatest earth scientists of the past century, two of whom, H. U. Sverdrup and C. G. Rossby, have phenomena named after them. In so doing, it became possible to assist in or even manage a wide variety of technological start-ups. Among these were initiating oceanographic forecasting services for amphibious landings and the offshore oil industry, creation of a “Worldwide Standardized Seismograph Network,” monitoring the ocean environment from space, establishment of an …

A Catalog of Old Spanish Seismographs

For more than a century seismographs have been the main source of data for seismological research. Their design principles and performance have significantly changed from the early seismoscopes to the present broadband instruments. Knowledge of their characteristics and evolution is important in two ways. Firstly, the history and evolution of seismological research is closely linked to the progress in developing appropriate instrumentation. Secondly, accurate knowledge of the periods of operation and recording parameters of old instruments allows us to reanalyze their records on the basis of modern algorithms and theoretical concepts and thus to obtain new results on older 20th-century earthquakes (Kanamori, 1988). Additionally, seismographs can be considered as a materialized resume of the theoretical and technical knowledge in seismology at a given time. The study of their characteristics and evolution gives a deep insight into the roots and historical development of seismological science (Dewey and Byerly, 1969 ; Ferrari, 1997). Some seismographs have been designed and constructed by eminent seismologists, and some seismologists got their reputation because they constructed good seismographs. The second objective is not an easy one. In the late 1950's and early 1960's, the global introduction of highly sensitive electrodynamic sensors with galvanometric photographic or electronically amplified recordings on paper or tape outdated almost every available instrument up to that time. The most conspicuous exponent, but not the only one, of that change was the deployment of the World Wide Standard Seismograph Network (WWSSN), which resulted in much more homogeneous global data coverage, significantly lowered detection thresholds, and improved earthquake location and catalog completeness. As a result, significant improvement of global seismicity patterns and understanding of their relationship to global plate tectonics, velocity models, and many other important seismological findings arose. But the real breakthrough came only in the 1980's and 1990's with the development …

Observation of mining-induced faults in an intact rock mass at depth

Stoping of a highly-stressed remnant in a deep South African gold mine was accompanied by considerable seismic activity and some significant rockbursts. The larger seismic events were registered some 60 km away at a World-wide Standard Seismograph Network (WSSN) station. Several shear ruptures were encountered subsequently in a tunnel driven to follow the mining faces. A careful study based on detailed exploration of two of these ruptures proved them to be the source of two of the larger rockbursts. The ruptures were essentially planar features of considerable areal extent with shear displacements of up to 100 mm of a normal dip–slip sense. Certain striking features were revealed by a scanning electron microscopic study of some of the fresh cataclastic rock-flour which formed part of the comminuted filling of these ruptures. These provided strong evidence for extremely violent fracturing phenomena in the faulting process. A proper understanding of these phenomena could provide useful insight into the source mechanism of rockbursts and the control of the accompanying damage. Because of the many similarities in morphology of the faults and in the nature of the seismic signals it could be argued that the rockburst rupture is a microcosm of the pristine earthquake. Understanding of the mechanics of the rockburst shear rupture might therefore have some relevance in the study of the earthquake source.

Revised world seismicity catalog (1950-1997) for strong (Ms≧ 6) shallow (h≦ 70 km) earthquakes

AbstractUsing the standard earthquake catalogs provided by the International Seismological Centre (ISC), its predecessor the International Seismological Summary (ISS), and the National Earthquake Information Center (NEIC), I analyze the worldwide consistency of teleseismic reporting, completeness of the seismicity record, and homogeneity of magnitude determination, for strong shallow earthquakes (surface-wave magnitude, Ms ≥ 6; depth, h ≤ 70 km) for the period 1950 to 1997. Under the postulates that the rate of earthquake occurrence for the entire world is constant on a time scale of decades and that well after the installation of the World-Wide Standardized Seismograph Network in the middle 1960s the earthquake catalog for strong (Ms ≥ 6) shocks is complete, and the seismicity rates are typical of all periods in the century, we find that, due to the use of different formulations and criteria to calculate the parameter magnitude, the Ms of moderate (6 ≤ Ms < 7) events during the period 1950 to 1963 was systematically overestimated by as much as 0.5 magnitude unit, relative to the Ms assigned to shocks occurring after 1963. When this correction is taken into account, the new catalog of events with Ms (corrected) ≥ 6 in the period 1950 to 1997 becomes largely homogeneous in Ms. Under the foregoing postulates, this new catalog is shown to list nearly all and only the strong shocks [Ms (corrected) ≥ 6; h ≤ 70 km] that occurred in the Earth during the period, a notable exception being the time span from 1964 to 1968. The revised catalog, including the scalar moment and moment magnitude for each event, is listed on the worldwide web page http://www.ldc.usb.ve/~ojperez/catalog.

Centroid moment tensor solutions for deep earthquakes predating the digital era: the World-Wide Standardized Seismograph Network dataset (1962–1976)

Centroid moment tensor solutions are presented for 104 deep earthquakes covering the years 1962–1976. These solutions are obtained by applying the algorithm used for modern events to restricted datasets of analog (WWSSN, World-Wide Standardized Seismograph Network) seismograms.