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3 GLOBAL NETWORKS REVIEW The history of global setsmographic networks* is closely tied to the U.S. national need for improved capability in detecting and identifying underground nuclear explosions. The World-Wide Standardized Seismograph Network (WWSSN) was established in the early l960s as a part of Project Vela Uniform, a program of fundamental and applied research in seismology managed by the Defense Advanced Research Projects Agency (DARPA). Since then DARPA has been responsible for virtually all advances in global seismographic networks, but has declined to commit funds for routine WWSSN operations. Key elements of the WWSSN are standardized three-component long- and short-period seismographs with uniform calibration, and the means for distributing the seismograms to the earthquake research community. The WWSSN today comprises ll0 stations operating in 54 countries; its role is to produce the data needed for fundamental research in seismology. The responsibility for installing and managing the WWSSN was assigned by DARPA to the U.S. Coast and Geodetic Survey (USCGS). The network was essentially completed by l963. The WWSSN serves as a worldwide organization base to which network improvements and modernization can be applied. The network was partially funded by the National Science Foundation (NSF) between l968 and l978. In l973 the WWSSN and other elements of the USCGS earthquake program, apart from the data services, were transferred to the U.S. Geological Survey (USGS) and, *See Appendix A for further information on the global networks.

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8 since l978, the network has been funded entirely by the USGS under the National Earthquake Hazards Reduction Program (NEHRP). Since the inception of the WWSSN, more than 5 million original seismograms have been microfilmed and 60 million high-quality film copies have been supplied to research workers by the Environmental Data Service of the National Oceanic and Atmospheric Administration (NOAA). Despite the superiority of the more recently available digital seismic data for many purposes, the analog seismograms from the WWSSN remain the foundation for much fundamental seismological research, not only in the United States but around the world. WWSSN encountered its first difficulty when attempts were made to transfer its financial support from the Department of Defense (DOD) to NOAA in the late l960s, a transfer that had been discussed and coordinated over a period of years. Opposi- tion centered on the U.S. support of the foreign stations of the WWSSN, and the NSF assumed the responsibility for partial support of the foreign stations of the WWSSN in l968. In the late l960s, DARPA sponsored the development and installation of l0 high-gain long-period (HGLP) seis- mographs. The HGLP seismographs were superior to the WWSSN seismographs in the detection of long-period earth motion because of their installation in special airtight tanks to protect them from temperature and pressure changes. The HGLP seismographs were also the first globally deployed seismographs to be equipped with digital recorders. The USGS was assigned responsibility for the HGLP network and managed it as a complementary part of the WWSSN. Later, five of the HGLP systems were modified: short-period seismometers were added, and the original digital recorders were replaced by more advanced, computer-controlled versions. The modified HGLP seis- mographs, now called Abbreviated Seismic Research Observatory (ASRO) systems, are still in operation. The HGLP seismographs, especially the horizontal com- ponents, are affected by earth tilt caused by atmospheric loading of the earth's surface by wind and variations in barometric pressure. The resulting ground noise is attenuated rapidly with depth. A joint effort by private industry and the government led to the successful development of a broadband low-noise force-balance accelerometer that could be installed in a small-diameter borehole. Operated at a depth of l00 m, the borehole seismometer is virtually unaffected by wind noise at the surface. In l973, the USGS, with DARPA funding, began

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the development and global deployment of l3 Seismic Research Observatories (SRO) that combined the new borehole seismometer with an advanced analog and digital recording system. The availability of high-quality digital data produced by the SRO stimulated utilization of digital data by many research organizations. New analytical techniques and software were developed, opening exciting new directions of research such as the determinations of source parameters for all large earthquakes in a given time interval. In the late l970s, again with funding from DARPA, the USGS developed a digital recorder that could be attached to existing WWSSN systems. Seventeen such recorders are currently being installed at WWSSN stations (termed DWWSSN stations). NSF has funded their installation at six foreign stations, and the USGS is funding installation at the remaining sites. ASRO, SRO, and DWWSSN stations have been termed collectively the Global Digital Seismograph Network (GDSN) and observatories are located in Figure l. The GDSN and the WWSSN are complementary networks and together have been termed the Global Seismograph Network (GSN). Operation of the GSN, with stations in more than 60 countries of the world, is a notable example of successful international scientific cooperation and data exchange. Hundreds of seismographic stations are operated by other countries that go into a total global seismographic network effort, and data from these are available to U.S. seismologists. There are many seismologists, both in the United States and in foreign countries, who do not have access to computer facilities and can work only with analog data, who prefer to work with analog data, or who need the denser global coverage of stations provided by the WWSSN. In its relatively short life, the WWSSN has generated an historical data base that is important as a baseline for testing new hypotheses; continuing data from many of the same stations are essential to eliminate the possible effects of station location on recordings of seismic events. The GSN would continue an infrastructure that stimulates and supports international cooperation in seismology. It now provides the USGS with convenient and ready access to seismological organizations in more than 50 countries. In many countries, the GSN stations represent the principal or only national facilities for support of in-country seismological programs. Termination of some WWSSN stations may have serious and long-lasting

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l0

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ll political as well as scientific repercussions. Even though numerous seismographic stations exist in many other countries, their data are not as readily available to the researcher as are GSN data because of the established data distribution system. While the SRO systems were being installed, the University of California at San Diego developed and began installing digitally recording gravimeters that are designed to record very-long-period vertical-component seismic data, including earth tides and free oscillations. Seventeen are currently in operation, and the network is called the International Deployment of Accelerometers (IDA). The digital data provided by the IDA network and distributed by NOAA are used by many research groups for very-long-period studies of the earth's structure and the earthquake source mechanism. Implementation of IDA has been funded by the National Science Foundation and a private source, but, as manager of GSN, the USGS has been suggested by NSF as the agency that can best provide long-term future support for the network. The role of DARPA is limited to the development and demonstration of new technology; hence DARPA support for the operation of the GDSN ended in FY l979 even though much DARPA-supported research today makes substantial use of GDSN data. Following recommendations set forth in the NRC reports entitled Trends and Opportunities in Seismology (NRC, l977b) and Global Earthquake Monitoring (NRC, l977a), the research community strongly urged that the USGS provide long-term operational support of the GDSN beginning in l980. Funding for the continued operation of the network by the USGS was planned in the report entitled Earthquake Prediction and Hazard Mitigation: Options for USGS and NSF Programs (NSF, l976), which outlines the structure of the National Earthquake Hazards Reduction Program (NEHRP), beginning in FY l980 under all budget options in the report. The recommendations were accepted, and, beginning in FY l980, the USGS has provided both management and funding of the GDSN. Network support operations are managed by the USGS Albuquerque Seismological Laboratory (ASL). ASL furnishes operating supplies routinely and replacement parts or components on call and repairs defective equipment returned from the stations. Contract maintenance technicians operating out of ASL install new equipment and service operating stations. Optimally, two or three maintenance teams are overseas at any given time and can

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l2 respond to provide assistance to stations. During routine service visits, the maintenance personnel perform tests, calibrations, and any software or hardware modifications that are required. In operating the WWSSN stations, participating organizations contribute 2 to 3 times more than the annual costs to the U.S. government. The most recent (to l982) development has been the installation of a five-station telemetered network by Sandia National Laboratories as part of a Regional Seismic Test Network (RSTN). The stations, which are unmanned, acquire signals from borehole seismometers (improved versions of the SRO sensors) and transmit nine channels of data continuously in three data bands: short-period, mid-period, and long-period. A geosynch- ronous satellite provides two-way communication between the network control station, located in Albuquerque, and each RSTN station. Current plans are to merge RSTN data (events only in the case of short- and mid-period signals) with GDSN data on the network day tapes for general distribution. RSTN data are also received and processed in the new DARPA Center for Seismic Studies (CSS) in Arlington, Virginia. The establishment of the WWSSN, and its subsequent development, was certainly one of the outstanding U.S. accomplishments in international support of science. It has been the major factor in developing seismology into a quantitative and precise science that provides much of our basic knowledge of the earth's structure, of the active processes that deform it, and of the hazards and risks of earthquakes. One can well argue that the revolution in the earth sciences that followed the recognition of plate tectonics derived from two main subfields, i.e., marine geology and seismology, and that the contributions from seismology derive largely from an analysis of WWSSN data. We have every reason to believe that advances in the coming decades will flow similarly from analyses of data from today's global networks. ASSESSMENT OF PROBLEMS Global networks have been plagued throughout their existence by the lack of sufficient long-term funding from a host organization within which the operation is viewed as a significant element and thus receives enthusiastic support. The funding problems of the WWSSN did not cease with its transfer to the new Branch of

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l3 Global Seismology of the USGS in l973. It now had to compete for its funding with other elements within the USGS of the large and underfunded NEHRP, and with the increasing support needed for the GDSN. Global networks, in the competition between USGS service- and mission- oriented programs, have been subject to funding pressures that annually threaten their stability and continuity. Within the broad USGS seismological research program, a fairly small fraction of scientists works with data from global networks, so that internal advocacy, while dedicated, represents a minority. Consequently, the maintenance of global networks, an important service to the seismological community, lacks universal support within the Survey. Despite this situation, USGS continues to support the GSN. In contrast, a large part of university-based seismological research on the earthquake process, earth structure, tectonics, and earthquake prediction relies heavily on the global networks. Thus many non-USGS seismologists depend upon that agency for service in providing high-quality global data while most USGS seismologists do not need such data for their research. This dichotomy produces competition between programs with strong Survey interest and those that provide services largely for non-Survey personnel. Nevertheless, USGS administrators have allocated funds for the maintenance of the WWSSN and to allow for the steady upgrading of the worldwide system by the addition of a digital capability, with support from DARPA and NSF. A serious problem exists in that global network funds have remained fixed for the past three years. This year, once again, the seismological community and the USGS have been faced with options to meet the budget ceilings.* These include reducing WWSSN, reducing GDSN, and obtaining more funds, the latter never succeeding despite strong efforts. The community has always reaffirmed its strong backing for retaining the capabilities represented by the WWSSN essentially as it now exists. This annual occurrence makes it clear that some means must be found to ensure the continuity of the WWSSN and its systematic upgrading into the digital era. The GSN should be insulated from the vagaries of funding of the NEHRP. Support for the GSN must be thought of in terms of decades and in terms of its international impact and in terms of the health of seismology. The *See Appendix A for details of global network options.

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l4 USGS must continue to meet its long-term commitment to the GSN, even if the NEHRP should be terminated. Given the time scale of processes controlling global seismicity, it is essential to establish and maintain a data base that is uniform for many decades. The major short-term problem thus rests with funding for the global system. Because of recent increases in the costs of supplies for the WWSSN and of maintenance required for the GDSN, it is becoming increasingly difficult for the USGS with inadequate program resources to maintain the present and the projected level of operation of these networks. On the other hand, diverse users in the seismological community require both analog and digital data with no interruption of continuity or coverage of either type of data. Eliminating either the WWSSN or the GDSN should not be considered an acceptable solution to current funding problems. (Absorbing a FY l983 $500,000 shortfall in this manner would represent a 35 to 40 percent reduction in the data collected.)* Seismologists do not consider the problem as one of analog versus digital data. Until very recently, analog seismograms constituted the fundamental data base of global seismology. Although analog records are more limited in dynamic range and more difficult to use for quantitative analysis than digital records, they appeal to the trained eyes of seismologists and other earth scientists more directly. Very often subtle changes in the waveform on analog records are used for the determina- tion of the depth of earthquakes and for information on the fine structure of the earth's interior. Initial hints that led to important discoveries have often been found in such features of analog seismograms. Analog records represent many more stations than digital records, and they can be utilized without sophisticated hardware and software.* Digital seismograms, on the other hand, are far superior to their analog counterparts when we know what parameters are to be extracted from them. A large number of data can be processed in a relatively short time to obtain accurate results. Over the past few years, the number of high-quality normal mode data and source mechanism solutions has increased by more than an order *See Appendix A for budgetary information. **See Appendix A for a discussion of the utility of analog data.

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l5 of magnitude, which brought about several major break- throughs in seismology. The basic fact of data superior- ity assures the ongoing conversion to digital acquisition of seismic data. The importance of the global data base to the seis- mological community is such that the overwhelming consensus of the workshop participants was that no stations should be eliminated with the possible exception of redundant WWSSN analog and GOSN digital stations. It is anticipated, however, that digital stations will eventually supplant the analog WWSSN stations at selected sites of the global network and that analog (microfiche) seismograms will be generated from the digital recordings. The remaining analog WWSSN stations should continue to operate until it can be demonstrated to the scientific community that they are no longer needed as part of the global data base. A third type of problem lies in the slow pace of utilization of the digital data. Because of the diversity of users and their in-house capabilities, there are difficulties in the transfer of technology in going from analog to digital recording. This includes instrumenta- tion changes, software development for users, and dissemination of information to users. Moreover, the flow of digital data to users is not yet adequate. Tutorial data packages on selected special events are needed, to allow researchers to gain experience with the new data at reasonable cost and to learn how to use them for their individual problems. High-technology, high-cost facilities transferred from one government agency to another create a fiscal problem for the receiving agency. We here refer to such transfers as that of the WWSSN from DOD to NOAA to the USGS; that of the SROs from DOD to the USGS; the pressures for transfer of IDA from NSF to USGS; and the possibility of a transfer of RSTN from DOE to USGS. The problem is not that the receiving agency is surprised by an unexpected request—in the above cases, transfers have been planned over a period of years. Rather, the problem is that base funding is almost never transferred along with the responsibility for the facility operation. The receiving agency thus gets the funding problem as part of the transfer. It should be emphasized that these transfers are usually regarded as the best alternatives to the government and to the science. The option of dismantling a valuable resource is not an acceptable alternative.

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l6 RECOMMENDATIONS It is essential to maintain a global data base that is uniform for years or even decades. This requires establishing a supportive home environment for GSN. Relevant U.S. government agencies must realize that a long-term commitment is implicit in the very existence of GSN, independent of the mission-oriented programs of the host organization. We suggest that a solution to the long-term problem may be to transfer responsibility for the global networks from its present NEHRP base to another location within the Survey or even to another agency so the GSN does not compete directly for funds within a largely unrelated program. In regard to the options open to the USGS over the short term, we recommend seeking funds to support the global networks at the required level from normal budgetary requests, from within the USGS, and from other agencies, such as DARPA, that use data from the networks. Should this fail, we recommend that efforts be directed toward maintaining the WWSSN at the present level at the expense of a slowdown in the completion of the GDSN program and of a data loss that may result from a reduced GDSN maintenance program. Consequences of this approach should be reviewed yearly. At the same time the USGS should seek assistance from other agencies in providing operational support during this difficult interim period. In particular, DARPA cannot ignore the pertinent role of the GDSN data base in DARPA objectives, and the serious degradation threatened by inadequate funding. The problem of digital data usage must be addressed while the demand for analog data continues to be met fully. Additional efforts are needed to familiarize seismological researchers with the use of digital data and associated software for analysis. Digital data will ultimately replace the analog WWSSN. Methods for better access to the data need to be developed, and new data products at reasonable cost to the user should be generated and provided by agencies responsible for data distribution to promote wider use of the data. The interagency transfer of network facilities is a remaining outstanding issue. The associated problems can be largely resolved if adequate funding is transferred along with the operational responsibility, as was done, for example, in the recent transfer of the strong-motion network from NSF to USGS.