1. Introduction

2. The current status of earthquake observations and surveys and related issues
(1) Current earthquake observation systems
(2) Current observations of crustal deformation

3. Guiding principles of interim observations and surveys
(1) Observations of micro earthquakes in inland areas
(2) Observations of crustal deformation (GPS continuous observation)
(3) Surveys of active faults

Sources:
Regarding the Establishment of the Panel on Observation and Survey Planning
Members List of the Panel on Observation and Survey Planning
Minutes from the Meetings of the Panel on Observation and Survey Planning

The Great Hanshin/Awaji Earthquake - the largest earthquake disaster in the post-World War II era - led to enactment of the Law Concerning Special Measures for Earthquake Disaster Prevention and establishment of the Headquarters of Earthquake Research Promotion. The Headquarters is in charge of planning comprehensive earthquake observations and surveys. Subsequently, this Panel was created to serve under the Headquarters' Policy Committee, and commenced its investigations in October 1995.
In planning for earthquake observations and surveys, the Panel examined several important issues that need to be addressed, taking into consideration the risk of earthquakes continuing to occur into the foreseeable future. This report includes a summary of the basic observations and surveys that should be conducted in the interim.
This Panel will investigate earthquake observation and survey plans in accordance with the views set forth in this report. Research will also be conducted into issues that have yet to be thoroughly reviewed, including: observations and surveys of ocean areas, the collection and distribution of observation and survey results, observation and survey systems, observations and surveys of the Tokai district, and other relevant issues. Table of Contents

The Japan Islands are located at the junction of the Pacific plate, the Philippine Sea plate, the Eurasia plate, and the North American plate. As a result, Japan experiences a high level of crustal activity. The Japanese have suffered numerous disasters in the form of huge interplate earthquakes caused by plate subduction and inland earthquakes accompanied by the inland fault activity caused by plate movements.
A wide range of earthquake observations and surveys in Japan have been conducted by various organizations and universities, adding to the body of knowledge regarding earthquakes. However, there has been a lack of adequate equipment to conduct nationwide observations and surveys, particularly to assess inland earthquakes, systems to collect and distribute observation and survey results, and schemes to implement these results.
In addition, another issue concerns the maintenance and prospective improvement of the detection capacity of an observation network that is being organized Tokai district. Table of Contents

The earthquake observation network in Japan consists of the nationwide network that monitors large, medium, and small earthquakes, and the micro earthquake observation network developed in each regional area.
The large, medium, and small earthquake observation network was organized in order to observe earthquakes with a magnitude of three or greater. This has allowed for the continuous accumulation of earthquake data across the nation. Furthermore, the Urgent Earthquake and Tidal Wave Detection Network was organized in 1993, improving earthquake detection capacity by placing the entire nation under the same observation network.
Furthermore, the micro earthquake observation network makes it possible to track of earthquakes of a magnitude of less than three. This network sheds light on the mechanisms of interplate and intraplate earthquakes, and serves as the basis for our understanding of earthquakes occurring in the Japan Islands and their environs. The micro earthquake observation network has been meticulously developed, especially in the southern Kanto district, where three plates overlap. The resulting research has helped to clarify the conditions regarding these overlapping plates.
Nevertheless, this type of observation network is limited to specified regions, such as the southern Kanto and Tokai districts, but no nationwide observation network has yet been organized. Efforts to establish a system to collect observation data from across the nation just began in 1995.
Earthquake observations in ocean areas are important for more accurate tracking of interplate earthquakes and other earthquakes occurring near the Japan Islands. At present, earthquake-related developments are monitored by observations on solitary islands, observations based on cable-type ocean bottom seismographs in the southern Kanto and Tokai districts, and temporary pop-up type ocean bottom seismographs. However, a continuous observation network covering a broad area has not yet been developed. There are still other issues regarding the improvement of observation technologies, including the need to develop an observation method that incorporates burying seismographs in the ocean bottom. Table of Contents

The observation of broad movements in the earth's crust as specifically related to earthquakes has previously been used as a geodetic surveying method. The results of successive surveys conducted since the Meiji era have helped clarify the status of distortions in the earth's crust in the Japan Islands, in addition to the conspicuous crustal deformation in the Izu Peninsula, Suruga Bay area, and other regions.
Originally introduced for the purpose of geodetic surveys, continuous observation by the Global Positioning System ("GPS") has played an increasingly important role with respect to earthquake monitoring in recent years. Compared to former geodetic survey methods, GPS makes it possible to instantaneously survey movements over broad areas. Initially, GPS was implemented in 1993 in the southern Kanto and Tokai districts as an additional method to observe crustal deformation. Now, GPS is eagerly anticipated to contribute to our knowledge of earthquake tectonics (including helping to promote a comprehensive understanding of various earthquake phenomena, such as crustal deformation, stress in the earth's crust, and geological structure). GPS enabled the prompt recording of the crustal deformation that accompanied the 1994 Hokkaido Toho-oki Earthquake (occurring off the eastern shore of Hokkaido), the 1994 Sanriku Haruka Oki Earthquake (occurring off the eastern shore of Aomori Prefecture), and the 1995 Hyogo-ken Nambu Earthquake. GPS has also played an important role in helping to understand the seismic activity surrounding the Izu Peninsula. Development of the GPS continuous observation network on a nationwide basis began in 1994.
The observation of crustal deformation occurring in ocean areas is expected to provide valuable information in regard to the long-term prediction of interplate earthquakes. At present, GPS observation of solitary islands, VLBI (very long baseline interferometry) observations, SLR (satellite laser range finder) observations, and other kinds of observations are performed on a continuous basis. However, the research and development of technologies to observe crustal deformation on the ocean bottom is still in its growth stage.
Additionally, facilities with equipment (including distortion meters and clinometers) for the continuous observation of crustal deformation are designed primarily to track short-term irregularities in crustal movements in specified areas centered on the southern Kanto and Tokai districts. (3) Current surveys of active faults
Active faults are the vestiges of past large-scale inland earthquakes. Since these faults have the potential to become active again in the future, surveys of active faults are an important means to assess the possibility of impending inland earthquakes.
Specifically, surveys of active fault regions are useful in determining areas where the potential exists for inland earthquakes. Furthermore, it is possible to estimate when periods of seismic activity will occur based on the average duration between prior periods of such activity. Therefore, surveys of past periods of seismic activity are valuable in predicting future inland earthquakes. Moreover, the scale of earthquakes resulting from active fault movement is related to the length of active faults and the amount of displacement. Therefore, understanding this information is helpful in predicting the scale of future inland earthquakes.
In the past, surveys of active faults have been conducted primarily by government research organizations and universities. Commonly-used methods of research have included: topographical and geological surveys, geophysical prospection, boring surveys, and trench surveys. As a result, with the exception of urban areas, the location and level of activity (the average rate of displacement) of active faults throughout the Japan Islands have largely been confirmed. Nevertheless, among the active faults that have been confirmed to exist, surveys of past activity that can serve as basic data to evaluate the potential of future inland earthquakes are presently limited. Finally, there is a limited amount of case studies regarding direct surveys (through the use of borings near active faults) of the stress in the earth's crust that causes earthquakes.
Surveys (including those done through boring) of ocean areas have recently commenced in order to investigate the distribution and history of active faults. Table of Contents

It has been more than a century since modern instruments were first used to conduct observations and surveys of earthquakes. This is a short interval compared to the estimated cycle of occurrence of large-scale interplate earthquakes, and is an extremely limited period compared to the time scale of activity in the earth's crust. Prior investigatory research has contributed to our knowledge of earthquakes; however, the accumulation of results from earthquake observations and surveys and the construction of the subsequent theories that are necessary to predict future earthquakes are still insufficient. Therefore, a greater focus on evaluation of earthquake potential from long-term view will require markedly strengthened observation and survey systems and accumulation of more data.
In order to obtain an objective understanding of seismic activity, the following measures are imperative: even and continuous nationwide observations and surveys, accumulation of basic data, and extensive sharing of survey results. As these surveys serve as the basis for understanding and evaluating seismic activity, they should be promoted in step with earthquake observations and surveys.
Based on the actual results of prior observations and surveys, and after reviewing fundamental observation and survey methods from the above perspective, this Panel recommends that the following items be observed and surveyed in inland areas: (1) micro earthquakes; (2) crustal deformation (monitored by GPS continuous observation); and (3) active faults. Furthermore, with regard to observations and surveys in ocean areas, we believe it is important to accurately understand seismic activity near plate subduction zones, and to track activity in the earth's crust on the Japan Islands and their environs. However, even though technically feasible, observations and surveys on the ocean bottom often entail problems. At present, there are only three cable-type ocean bottom seismograph in operation (three more are currently being provided for), so methods to observe crustal deformation in ocean areas are still in the research stage. Accordingly, observations and surveys in ocean areas will continue to be the subject of future investigation. Table of Contents

A precise micro earthquake observation network is expected not only to improve our accuracy in determining the hypocenter of inland earthquakes, but also to contribute to our store of knowledge regarding the detailed structure of the parts of the earth's crust that are hidden in faults and changes in stress in the earth's crust. Additionally, this system will hopefully improve our understanding of the distribution of stresses and the plate structure in deep portions of inland areas by providing accurate and extensive information about earthquake hypocenters and the conditions that spark earthquakes (i.e., the status of fault movements that caused an earthquake at the hypocenter). Moreover, this network should help explain the mechanisms that lead to interplate earthquakes in deep portions of inland areas.
The scale of inland earthquakes usually corresponds to the size (length and width) and degree of displacement of faults that have become active. Even if the length and degree of fault displacement cannot be estimated, the largest possible fault widths can be assessed empirically by determining the maximum depths at which inland earthquakes occur through micro earthquake observation. This method is also expected to be useful in estimating the scale of the largest possible earthquake in each regional area. These purposes determine the appropriate density of a micro earthquake observation network.
Prior observations indicate that inland earthquakes normally occur within a depth of 15 to 20 kilometers of the upper portion of the earth's crust in inland areas. Generally, in order to accurately determine the depth of an earthquake's hypocenter, it is desirable to have observation points located at intervals of a distance comparable to the depth of the hypocenter. Accordingly, at present, we believe it is appropriate to build micro earthquake observation facilities with equipment throughout the nation at horizontal intervals of between 15 to 20 kilometers.
Such an observation network will also allow us to improve our methods for determining the hypocenters of shallower earthquakes. Table of Contents

In order to assess the changes in stresses in the earth's crust that cause earthquakes, it is necessary to observe distortions in the earth's crust over broad areas. Owing to the nationwide development of the GPS continuous observation network, together with prior existing geodetic survey methods, changes in terms of time and space to distortions in the earth's crust can be tracked instantaneously and regularly over wide regions. Using this observation network, it is expected that information about changes in stresses in the earth's crust and accumulated distortions that might lead to earthquakes will be able to be stored. Finally, in conjunction with the results of earthquake observations, the network can also assist in the accumulation of knowledge regarding earthquake tectonics and the mechanisms that lead to earthquakes.
In order to acquire further knowledge of crustal deformation, high-density GPS continuous observation facilities with equipment need to be implemented over a broad area. However, distortions in the earth's crust across the nation, excluding areas where crustal deformation is particularly prominent, are accumulated annually on the order of 1 in 10,000,000. Therefore, it is appropriate to, for the time being, track crustal deformation over these broad areas through means of the conventional GPS continuous observation system. Specifically, in order to track the accumulation of distortions in the earth's crust within acceptable limits of error, GPS continuous observation facilities with equipment should be built at horizontal intervals of between 20 to 25 kilometers throughout the country. Furthermore, observation can appropriately be carried out in conjunction with existing geodetic survey methods.
A high-density GPS continuous observation network makes it possible to instantaneously track crustal deformation occurring in the aftermath of earthquakes, so this will hopefully continue to yield fundamental knowledge about the formation of earthquakes. In the case of the Hyogo-ken Nambu Earthquake (that led to the Great Hanshin/Awaji Earthquake of 1995), the underground Rokko fault system was active along approximately 50 kilometers, and an earthquake fault more than 10 kilometers was observed on the surface of the Nojima fault line. A high-density GPS continuous observation network is also helpful to instantaneously track crustal deformation occurring in connection with inland earthquakes in the magnitude 7 class.
In light of the results obtained from this type of observation network, we are planning to renew investigations regarding further increases in the density of GPS continuous observation facilities. Furthermore, we believe it is advisable to conduct these investigations together with continuous observations of crustal deformation using distortion meters, clinometers, and other current equipment. Table of Contents

The location and activity level of active faults in land areas has generally been confirmed. However, in order to make long-term predictions of inland earthquakes, it is necessary to clarify, in detail, the location and history of active faults, the faults' length, and the degree of displacement accompanying a single case of activity by means of topographical and geological surveys, geophysical prospection, boring surveys, trench surveys, and related investigations. At present, surveys should emphasize faults with a high level of activity that are considered to have the potential to cause large-scale earthquakes and on active faults located near urban areas.
Finally, we are planning the following: research and development of survey methods for latent faults in large urban areas and direct assessments (by the use of borings) of stresses in the earth's crust near active faults; improvements in surveys of active faults in ocean areas and in surveys of both active faults and the patterns of activity by surveying topographical changes; and the development of a research environment to conduct surveys of active faults, including the preparation of analytical instrumentation. Table of Contents

Regarding the Establishment of the Panel on Observation and Survey Planning

August 28, 1995

Policy Committee

We are planning to examine advisory policies concerning the promotion of earthquake observation and survey research, and have established this Panel on Observation and Survey Planning towards the goal of organizing such investigation. We will hold meetings to discuss the matters listed below. As necessary, the Panel will notify the results of these deliberations to the Policy Committee.

1. Matters for deliberation:

(1) Matters concerning the preparation of observation facilities with equipment for earthquake activity, crustal deformation, and similar developments;

(2) Matters concerning surveys of active faults and other items; and

(3) Other matters concerning recommendations for earthquake survey research.

2. Members of the Panel:

The Chairman of Committee will designate regular members and expert members of the panel separately.

Members List of the Panel on Observation and Survey Planning

Chairperson of Panel:
Akira Hasegawa (Professor, Faculty of Science, Tohoku University)

Panel Members:
Masataka Ando (Professor, Disaster Prevention Research Institute, Kyoto University)
Hiroshi Ishii (Professor, Earthquake Research Institute, University of Tokyo)
Atsumasa Okada (Professor, Graduate School of Science, Kyoto University)
Yoshimitsu Okada (Director, Research Center for Earthquake Prediction, National Research Institute for Earth Science and Disaster Prevention)
Yasuhiro Ganeko (Director, Planning Division, Hydrographic Department, Maritime Safety Agency)
Yoshihiro Kinugasa (Chief Senior Researcher, Geological Survey of Japan)
Hajimu Kinoshita (Director of Deep Sea Research Department, Japan Marine Science and Technology Center) Ryuji Kurihara (Director, Seismological and Volcanological Management Division, Seismological and Volcanological Department, Japan Meteorological Agency)
Koichi Tsukahara (Head, Crustal Dynamics Department, Geographical Survey Institute)
Yukio Hagiwara (Professor, Nihon University, College of Humanities and Science)
Tomoo Hirasawa (Professor, Faculty of Science, Tohoku University)
Yoshimori Honkura (Professor, Faculty of Science, Tokyo Institute of Technology)

Minutes from the Meetings of the Panel on Observation and Survey Planning:
October 16, 1995 The first meeting of the Panel on Observation and Survey Planning
November 9, 1995 The second meeting of the Panel on Observation and Survey Planning
November 29, 1995 The third meeting of the Panel on Observation and Survey Planning
December 19, 1995 The fourth meeting of the Panel on Observation and Survey Planning
January 10, 1996 The fifth meeting of the Panel on Observation and Survey Planning

Active Fault Survey Working Group:
October 25, 1995 The first meeting of the Active Fault Survey Working Group
November 21, 1995 The second meeting of the Active Fault Survey Working Group

Fig. Seismic Observation Network in Japan
Top: Seismic Observation Facilities as of 1995
Bottome: Trial Calculation under 20km mesh

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