Preface                                          


This publication contains a list of origin times,
hypocenters, and magnitudes of 70,000 earthquakes 
occurring in the Kanto area and its vicinity 
during the period from June 1971 through September 
1980. Maps showing the distribution of these 
earthquakes are also presented. The focal 
parameters and their standard errors have been 
computed using data recoded by the network of 
highly sensitive seismograph stations of the 
Earthquake Research Institute with additional data
supplied from several institutions on an exchange 
basis. Many members of the ERI have been involved 
in the observation and data processing of these 
earthquakes. Among them Dr. K. Tsumura, now at the 
Japan Meteorological Agency, took a leading role.

Dr. R. S. Matsu'ura and Mr. I. Karakama have 
reexamined the records and redetermined or newly 
determined the hypocenters employing an algorithm 
developed by Dr. M. Matsu'ura of the Geophysical 
Institute, University of Tokyo. The output of the 
focal parameter computations has been printed here 
in two parts. The 400 km x 500 km area covered by 
this catalog is a most complex and interesting 
zone in view of the seismotectonics of Japan. It 
is our hope that this catalog will be used as a 
primary data source for various kinds of 
earthquake studies.

                    Tokuji Utsu
                    Director
                    Earthquake Research Institute


           Additional Information

In any oral or written presentation including
these data, please reference:

R. S. Matsu'ura, I. Karakama, and K. Tsumura,
  List of Earthquakes in the Kanto area and
  its vicinity for June 1971-September 1980,
  Part 1, Earthquakes Research Institute,
  University of Tokyo, 1988.
        
R. S. Matsu'ura, I. Karakama, and K. Tsumura,
  List of Earthquakes in the Kanto area and
  its vicinity for June 1971-September 1980,
  Part 2, Earthquakes Research Institute,
  University of Tokyo, 1988.

DATA FORMAT for files of List 1, 3, and 4:
  (5I2,F4.2,I3,2F3.1,F6.4,F3.1,F7.4,F3.1,F5.2,
   F3.1,3I2)
year-1900, month, day, hour, min., sec., IT, 
Mf-p, Mamp, latitude in degrees, DY in km, 
longitude in degrees, DX in km, depth in km, 
DZ in km, number of stations, iteration number, 
number of region in List 5.

The smaller the number of iterations (IT), the better 
the obtained hypocenter is and the less the 
result depends on the initial guess.

If you find any error in the digital data, please
write to R. S. Matsu'ura:

   3-10-9-401 Umegaoka
   Setagaya
   Tokyo 154 JAPAN


        Index to the List of Earthquakes

                      Part 1

Introduction                                     1
Notations                                        5
List 1. Well-converged hypocenters - part 1      7
            (June 1971 - December 1976)
Figure 1. Maps of epicenters - part 1          502
            (June 1971 - December 1976)
List 2. Stations                               570
Figure 2. Maps of stations                     573


                      Part 2

Notations                                        1
List 3. Well-converged hypocenters - part 2      4
            (January 1977 - September 1980)
Figure 3. Maps of epicenters - part 2          445
            (January 1977 - September 1980)
List 4. Hypocenters not well-converged         491
Figure 4. Yearly maps of epicenters            506
List 5. Regions                                516
Figure 5. Map of regions                       517
List 6. Interruption of observation at the     518 
           five stations of Dodaira 
           microearthquake observatory
List 7. The program for the hypocenter 
           determination                       522



        Notations for Lists 1, 3, and 4

D   H    M      S        Origin time of an 
day hour minute second   earthquake (Japan 
                         Standard Time).

 MAG      Magnitudes determined from the
F-P AMP   duration time (F-P), and the maximum 
          amplitudes (AMP).

 LAT      North latitude of an epicenter in
D M S     degree, minute, and second.

DY        Epicentral error in the north-south 
          direction in KM.

LONG      East longitude of an epicenter in  
D M S     degree, minute, and second.

DX        Epicentral error in the east-west 
          direction in KM.

DEPTH     Focal depth in KM.

NS        Number of stations where seismic waves 
          are detected.

NR        Region number listed in List 5 and shown 
          in Fig. 5.

*         An artificial earthquake or an explosion.


                        Notations for List 2

CODE      Station code.

ORG       Organization to which a station belongs.
   ABU: Abuyama Seismological Observatory, 
         Kyoto University
   CRI: Central Research Institute of Electric 
         Power Industory
   DPR: Disaster Prevention Research Institute, 
         Kyoto University
   ERI: Earthquake Research Institute, University 
          of Tokyo
   HKD: Hokkaido University
   IIS: International Institute of Seismology and 
         Earthquake Engineering
   JMA: Japan Meteorological Agency
   NGY: Nagoya University
   NRC: National Research Center for Disaster 
         Prevention
   THK: Tohoku University
   TKY: Faculty of Science, University of Tokyo
   UTS: Utsunomiya University

NAME      Station Name.
 
LAT       North latitude of a station in degree.
 
LONG      East longitude of a station in degree.
 
H         Station height in kilometers.
 
COR       Station correction (in seconds) used for 
          the hypocenter determination.
             
TERM      The term during which data of a station 
          is used for this work (not always equal 
          to the operating term of the station).

SEN       The total gain of observation on the 
          monitor (kine/mm).

DATE      The date when the amplifier gain was changed.
 

                        Notations for List 6

M     D   H    M        Starting and ending time 
month day hour minute   of a problem.
 
    ST.           D: DDR
D K O S T         K: KYS
                  O: OYM
                  S: SRY
                  T: TSK

A problem occurred at stations marked by * or #.

  *: Power failure, radio problem, or other 
     problems of electric signals. No substitute 
     was available.

  #: Improper pen pressure, ink shortage, 
     occasional grazing pen, or other problems in 
     recording. Other monitoring instruments were 
     occasionally used as a substitute.



                Introduction

In order to reveal the mechanism of earthquake 
occurrence and to achieve the scientific 
earthquake prediction, the study of 
microearthquakes is very important. The 
construction of microearthquake observation 
networks and the improvement of the data 
acquisition and processing systems for those 
networks have been from the beginning a major 
part of Japan's national project for earthquake 
prediction. With data obtained by those networks,
research has been done on many notable seismic 
activities and published in the Report of the 
Coordinating Committee for Earthquake 
Prediction or other publications. However, data 
from microearthquake observation networks have 
been rarely utilized for studying seismicity 
features for a longer term. The earthquake catalog 
of the Japan Meteorological Agency (JMA) is mainly 
used for this kind of study even now.

Valuable data from microearthquake observation 
networks must be used not only for the analysis of 
individual activities, but also for extracting 
universal features of earthquake occurrences. For 
the latter kind of research, data from a network 
operated continuously over a long interval of time 
are desirable. Few such data have been published 
from microearthquake networks.

This work contains lists of earthquakes which 
occurred in the Kanto area and its vicinity during 
the 1970's, when the Earthquake Research Institute 
(ERI) was most exclusively engaged in the 
detection of microearthquakes in the area. It is 
based on the microearthquake data set prepared by 
correction, amendment, modification, 
supplementation, and revision of about 400,000 
cards of the routine data by referring original 
seismograms in storehouses. Hypocenters in the 
lists are newly determined from these new data.
 
i) Data

For the hypocenter determination, data from 
stations in List 2 and Figure 2 are used. The 
basic stations among them are the following:

   1) Stations of Dodaira Microearthquake 
      Observatory (DDR, KYS, OYM, SRY, TSK)
      Signals were radio telemetered and recorded 
      at ERI on long-term drum recorders (paper 
      speed 4mm/sec, tick marks every second).

   2) Stations operated by the fund for the South 
      Kanto Project (HAT, HNG, INB, KBH, OKN, TKE)
      Signals were recorded at individual sites on 
      drum recorders (paper speed 4mm/sec, tick 
      marks every second).

   3) Stations of the Seismological Mobile Survey 
      of ERI in the Izu Peninsula
      (DSZ, HGW, HOK, ICY, KWZ, NGH, NRM)
      Recording system was the same as 2).

   4) Stations of Fujigawa Crustal Movement 
      Observatory of ERI (FUJ, UMJ)
      Signals were recorded and data were read in 
      the observatory.

Maintainance of these observations was done by the 
following ERI staff members: Kenji Kanjo, Ikuo 
Karakama, Hideteru Matsumoto, Isao Nakamura, Izumi 
Ogino, Masayoshi Takahashi, Masaru Tsujiura, 
Kenshiro Tsumura, and Shigeru Watanabe. The data of 
arrival times and other parameters were read 
routinely by Kenshiro Tsumura for the period June 
1971-August 1972, and by part-timers for the rest
of the time. Data supplied from stations of the
National Research Center for Disaster Prevention 
(NRCDP) on a mutual exchange of basis were 
included for the period July 1971-February 1979. 
In addition to these data, data from many 
temporary stations and temporarily exchanged data 
with other universities or organizations were 
mixed with the routine data.

We first mixed data from JMA stations in List 2 
taken and these data were examined. For data of 
1980, part of NRCDP data was also mixed from the 
Seismological Bulletins of NRCDP. Since the data 
processing in those days was done on an off-line 
basis and much manual labour was involved, there 
were a lot of mistakes and problems in the data. 
We marked data of teleseismic signals and 
excluded phantom local earthquakes. We also marked 
apparent explosions in quarries or other 
artificial earthquakes. (Those explosions are 
marked by an asterisk in the lists and excluded 
from all the figures.) One-minute difference among 
data using different clocks often resulted in 
duplicate counts of an earthquake. In addition to 
these errors, various kinds of errors are 
corrected.  Almost 40% of the cards were subjected 
to some change. Those changes were made by
referring original records when they were 
available.  Every page of stripchart records 
(paper speed 60mm/min) for the stations in 1) 
were also examined to recover omitted data and 
about 50,000 data records were added to correct 
deficits in the old data. In List 6, interruptions 
of observation at the stations in 1) (the most 
fundamental stations in the network) are listed 
for the sake of time-series analysis.
 
ii) Hypocenter determination
 
Mikumo's model E-3A3 (1966) is used as the 
velocity structure for the calculation. This model 
is often used for the Kanto area, and the old 
routine also used it. However, for the areas far
from the Kanto area, this model does not represent 
the structure well.  Therefore, earthquakes 
located outside of the area defined by [32.5 N, 
37.5 N] and [137.8 E, 142.2 E] were excluded from 
List 1 and List 3. Station corrections (Ishida and 
Asano, 1979) for this model are used in the 
calculation.

The old routine method of hypocenter determination 
had some problems. The origin time of an 
earthquake was fixed in the calculation. Errors of 
data were not appropriately treated in the 
calculation. Epicenters were often distributed on 
stripes with a space determined from the data 
accuracy. When a hypocenter came above the earth's 
surface during the iteration, the focal depth was 
fixed at 5 km. This resulted in diffusing 
hypocenters and in an obscure image of seismicity.

In the present work, a new method (Matsu'ura, 
1984) is used for the hypocenter determination. 
In this method: 1) prior information on the 
hypocenter is used, 2) the origin time is 
determined after the hypocenter is located, and 
3) errors in each datum are carefully treated in 
the algorithm, and no jump of a hypocenter 
location due to a false datum occurs. It is robust 
and only 1.4% of all hypocenters are not well-
converged due to lack of good arrival time data. 
These poorly converged hypocenters are listed 
separately in List 4 for future revision. The list 
of computer program for the hypocenter 
determination is shown in List 7. The program is 
available upon request.
 
As prior information for the calculation (an 
initial hypocenter and assumed errors), we use 
the following:

  1) For shallow earthquakes in the aftershock 
     area of the 1974 Izu-hanto-oki earthquake: 
     34.6 N +/- 40 km, 138.8 E +/- 40 km, 
     5 km +/- 5 km.

  2) For shallow earthquakes in the aftershock 
     area of the 1978 Izu-Oshima-kinkai 
     earthquake: 34.75 N +/- 40 km, 139.1 E +/- 
     40 km, 5 km +/- 5 km.

  3) For other shallow earthquakes in the Izu 
     area: 34.88 N +/- 40 km, 139.05 E +/- 40 km, 
     5 km +/- 5 km.

  4) For shallow earthquakes near Kobugahara 
     station: 36.65 N +/- 20 km, 139.4 E +/- 20 
     km, 5 km +/- 5 km.

  5) For shallow earthquakes in the Matsushiro 
     area: 36.5 N +/- 20 km, 138.2 E +/- 20 km, 
     5 km +/- 5 km.

  6) For other shallow earthquakes, the initial 
     epicenter is assumed to be 0.1 north and 0.1  
     west from the nearest station, the epicentral 
     errors are assumed to be 50 km, and the 
     initial depth and its error are assumed to be 
     20 km.

  7) For earthquakes in the aftershock areas of 
     the 1972 Hachijojima-kinkai earthquake and 
     the 1972 Hachijojima-toho-oki earthquake: 
     33.5 N +/- 50 km, 141.0 E +/- 50 km, 50 km 
     +/- 30 km.

  8) For other earthquakes, the initial hypocenter 
     is set as a hypocenter obtained by the 
     calculation from the first three P-arrival 
     times with the semi-infinite half space of 
     Vp = 6 km/sec, and the epicentral errors and 
     the error in depth are assumed to be 50 km. 
     When the initial depth is 30 km or shallower, 
     its error is assumed to be 30 km.

All earthquakes were located for which the onset 
of P-wave was detected at three or more stations, 
except ones whose S-P time at the nearest station 
was larger than 40 seconds. About 70,000 hypo- 
centers are listed in List 1 and List 3. The 
number of hypocenters is increased by 30% from the 
old routine result. In Figures 1, 3, and 4, 
hypocenters in these lists within the range of 
magnitude 0 or above, depth 300 km or shallower 
are plotted monthly and yearly. In the first pages 
for Figures 1 and 3, hypocenters for the entire 
period of List 1 and 3 are also shown. From these 
maps, a clear seismic gap is seen near the 
Boso Peninsula.
 
iii) Magnitude

The magnitude of an earthquake is determined from 
the total duration times (Tsumura, 1967) according 
to Hori's formula (1973).
 
       M    = 2.94 log (F-P     ) - 2.56
        F-P                (sec)

The magnitude is also determined from the maximum 
amplitudes. For velocity amplitudes, Watanabe's 
formula (1971) is used. For displacement 
amplitudes, Tsuboi's formula (1954) is used for 
earthquakes of depth 60 km or shallower, and 
Katsumata's formula (1964) is used for deeper 
earthquakes.
 
We are grateful to Prof. Tokuji Utsu for helpful 
suggestions, continuous encouragement throughout 
this work, and critical reading of the manuscript. 
Computations and data processing were done with a 
HARRIS H-300 at the Seismological Mobile Survey of 
the Earthquake Research Institute, University of 
Tokyo. Authors strongly hope that following this 
publication, earthquake lists from many 
microearthquake networks become available to the 
seismological community.
 
                 References

Hori, M., Determination of earthquake magnitude of 
  the local and near earthquake by the Dodaira 
  microearthquake observatory, Res. Notes Earthq. 
  Res. Inst., Univ. Tokyo, 10(4), 1-4, 1973 (in 
  Japanese).
   
Ishida, M., and S. Asano, A new seismicity map in 
  the Kanto District, Japan, J. Phys. Earth, 27, 
  435-453, 1979.

Katsumata, M., A method to determine the magnitude 
  of deep-focus earthquakes in and near Japan, 
  Zisin II, 17, 158-165, 1964 (in Japanese).

Matsu'ura, M., Bayesian estimation of hypocenters 
  with origin time eliminated, J. Phys. Earth, 32, 
  469-483, 1984.

Mikumo, T., A study on crustal structure in Japan 
  by use of seismic and gravity data, Bull. Earthq. 
  Res. Inst., Univ. Tokyo, 44, 965-1007, 1966.

Tsuboi, C., Determination of the Gutenberg-
  Richter's magnitude of earthquakes occurring in 
  and near Japan, Zisin II, 7, 185-193, 1954 (in 
  Japanese).

Tsumura, K., Determination of earthquake magnitude 
  from total duration of oscillation, Bull. 
  Earthq. Res. Inst., Univ. Tokyo, 45, 7-18, 1967.

Watanabe, H., Determination of earthquake 
  magnitude at regional distance in and near 
  Japan, Zisin II, 24, 189-200, 1971 (in Japanese).