From: andy@pangea.Stanford.EDU (Andy Michael USGS Guest)
Newsgroups: sci.geo.geology,ca.earthquakes
Subject: N. CA, USA, and World Quake Report 01/14-01/20/93
Date: 22 Jan 1993 01:23:11 GMT
Organization: Stanford Univ. Earth Sciences
Distribution: world
NNTP-Posting-Host: pangea.stanford.edu

DISCLAIMER -- THIS IS NOT AN EARTHQUAKE PREDICTION OR WARNING!
  The commentary provided with these map(s) is for INFORMATIONAL
USE ONLY, and SHOULD NOT be construed as an earthquake prediction,
warning, or advisory.  Responsibility for such warnings rests with
the Office of Emergency Services of the State of California.
PLEASE REMEMBER -- THIS IS PRELIMINARY DATA
  Releasing these summaries on a timely basis requires that the
data, analysis, and interpretations presented are PRELIMINARY. Of
necessity they can only reflect the views of the seismologists who
prepared them, and DO NOT carry the endorsement of the U.S.G.S.
Thus while every effort is made to ensure that the information is
accurate, nothing contained in this report is to be construed as
and earthquake prediction, warning, advisory, or official policy
statement of any kind, of the U.S. Geological Survey, or the
U.S. Government.
FOR QUESTIONS CONCERNING THIS REPORT
  Send e-mail to andy@pangea.stanford.edu


Seismicity Report for Northern California,
the Nation, and the World for the week of
 January 14 - 20, 1993

Data and text prepared by
  Steve Walter, Barry Hirshorn, and Allan Lindh
U.S. Geological Survey
345 Middlefield Rd.  MS-977, Menlo Park, CA  94025
Graphics by Quentin Lindh

San Francisco Bay Area  
    
  During the 7-day period ending at midnight on Wednesday, January 20,
1993 the U.S. Geological Survey office in Menlo Park recorded 32
earthquakes of magnitude one (M1) and greater within the San Francisco Bay
area shown in Figure 1.  This included a M5.0 event on the Calaveras, the
largest Bay Area earthquake since a pair of M5 Loma Prieta aftershocks
occurred east of Watsonville in April, 1990.  We recorded a M3 on the
northern Hayward fault and a fairly active sequence on the San Andreas
just southwest of San Juan Bautista that produced six M2 earthquakes. 
This total compares to 22 earthquakes that were recorded during the
previous 7-day period, four of which were as large as M2. 
  The Calaveras earthquake occurred Friday night about 6 miles east-
northeast of Gilroy (#3 in Fig.1).  It was felt as far away as Sacramento, 
Monterey, and Modesto, as well as throughout the Bay Area.  The earthquake
produced no injuries and little or no damage according to press reports. 
It was not preceded by any foreshocks and produced very few aftershocks. 
Of the three aftershocks recorded in the first two hours after the
earthquake, only one was as large as M1.  Ten more aftershocks were
recorded during the next five days, the largest a M2.4 early Wednesday
morning. 
   This was the largest earthquake on the Calaveras fault since a M5.0
event occurred in the Alum Rock area on April 3, 1989 .  It was
significant to seismologists because it occurred along one of two zones
considered "to be the most likely sites for the next M > 5 earthquakes". 
This earthquake "forecast" was included in an article published in 1990 in
the Journal of Geophysical Research (Vol. 95, No. B6) by Oppenheimer,
Bakun, and Lindh.  They observed that gaps in M < 3 seismicity coincided
with regions of the fault which ruptured during mainshocks.  One such gap
existed at the site of the January 15 event, which was also the site of a
similarly sized earthquake in March, 1949.  Based on the elapsed time
since that earthquake and the rate of movement on the Calaveras fault,
they speculated that this would be a likely site for the next M > 5
earthquake on the fault.
   Other earthquakes of interest include a M3.0 last Friday morning on the
northern Hayward fault, about 2 miles north of Berkeley (#1/1).  Although
the Hayward is generally quiet, this is one of several zones on the fault
that experience occasional earthquakes, some as large as M4.  The most
recent earthquake of comparable size in this area was a M3.2 on December
13, 1991.  The San Andreas fault was also quiet, with the exception of a
cluster of M2 events on the creeping segment southwest of San Juan
Bautista (#4/1).  Between Saturday morning and Monday evening, a total of
nine earthquakes > M1 occurred here; six of these were as large as M2. 
This is the same zone that was active in early December of last year.   
  
Northern California

    Northern California experienced quite a number of M2-3 earthquakes,
both along the San Andreas/Coast Range faults and in the northern Sierra
Nevada area.  This is in contrast to both central California, which
experienced only one M2 earthquake (a M2.4 that occurred along the coast
about 8 miles northwest of San Simeon (#2/2)), and eastern California,
where the only notable earthquake was a M3.1 about 30 miles south of Lone
Pine.  
   In northern California, the San Andreas was active near Point Arena,
where a M2.3 occurred early Saturday morning (#4/2), and in the Cape
Mendocino area, where three M3 earthquakes occurred during the week
(#3/2).  The adjacent Maacama fault was also active, both at it's
northern end with a pair of M2 events (#8/2) and at it's southern end
where a M2.2 event occurred about 3 miles northeast of Cloverdale. The
Geysers area, just east of the latter "Cloverdale" event, was also
slightly more active than normal, producing two M3.5 events late Monday
afternoon (#9/2).  Finally, a M2.7 occurred north of Clear Lake, near Lake
Pilsbury (#5/2). 
   The northern Sierra Nevada produced several notable earthquakes, the
largest a M3.2 Saturday evening about 7 miles east of Quincy (#7/2).  A
M2.8 occurred about this same time northeast of Red Bluff and was followed
by two more M2 events in the next three days (#6/2).   Other M2
earthquakes include a M2.2 11 miles southeast of Red Bluff, a M2.1 south
of Lake Almanor, and a M2.5 13 miles northwest of Truckee (#1/2).  
     
Long Valley Caldera
    
    There were numerous M1+ earthquakes in the south moat area during the
week, most in the western end just southeast of Mammoth Lakes.  However,
only one earthquake was as large as M2, a M2.2 event that occurred last
Thursday morning near the northern end of the Hilton Creek fault (#1/3).
Activity south of the caldera was also limited to events smaller than M2.
 
USA Seismicity

   According to information provided by the National Earthquake
Information Service, there were several earthquakes of note in the lower
48 states, in addition to those in California.   The first of these was a
M3.1 last Thursday that occurred in northern Oklahoma, near the Nebraska
border (#1/4).  This small earthquake was felt in the Oklahoma towns of
Cherokee, Helena, Jet, and Nash.  Later the same day another M3.1 occurred
in southeastern Tennessee (#2/4); it was felt in the Chattanooga-Cleveland
area and also across the border in northern Georgia.  Last Friday morning
a M4.2 occurred in central Nevada, west of the town of Eureka (#3/4). 
Just after midnight on Saturday a M4.0 earthquake occurred in the central
Gorda plate, off the southern coast of Oregon (#4/4).  Finally, a pair of
M3 earthquakes were recorded in southern California, aftershocks to the
M7.5 Landers earthquake of June, 1992. 
            
The Planet Earth
 
  The largest and most damaging earthquake during the past week occurred
in the Hokkaido, Japan region (#1/5).  This Mb6.9 event killed one person
and injured at least 364 other with damage at Kushiro, Hokkaido, and
Hachinohe, Honshu.  Later in the week, a Mb6.0 earthquake occurred beneath
the Sea of Japan (#5/5).  Other notable earthquakes in the southwest
Pacific include a Mb5.8 in the Mariana Islands (#3/5) and a Mb6.2 beneath
the Indonesian Island of Sumatera (#6/5).   A Mb5.7 occurred in central
Xijang (Tibet) that was felt at Lhasa (#4/5).  
   In the western hemisphere there was a Mb4.4 in the Virgin Islands, a
Mb4.9 near the coast of Nicaragua, and a Mb4.3 in central Alaska that was
felt at Fairbanks (#2/5).  
 
             Table 1.  Central California Seismicity (M>2.0)

--ORIGIN TIME (UT)-- -LAT N-- --LON W-- DEPTH  N N RMS ERH ERZ       DUR
YR MON DA HRMN  SEC  DEG MIN  DEG  MIN    KM  RD S SEC  KM  KM REMKS MAG

93 JAN 14 1242 38.40 39 27.25 120 21.17 10.64 10   .07 3.0 3.5 WAK   2.5
93 JAN 14 1817 22.04 37 36.87 118 48.86  5.04 29   .15  .4  .6 HCF   2.2
93 JAN 14 1959 11.53 35 43.06 121 18.25  9.51 35   .14  .7 1.1 SSM   2.4
93 JAN 15  557  0.19 40 25.42 124 25.49 11.86 12   .09 1.4  .4 MEN   3.0
93 JAN 15 1113 49.15 37 54.77 122 17.19  6.57 82   .17  .2  .5 HAY   3.0

93 JAN 16  629 35.07 37  1.14 121 27.74  7.28103   .14  .2  .4 CYS   5.0
93 JAN 16 1036 49.11 38 50.61 123 39.20  0.07  9   .09 1.6 4.4 PAR * 2.3
93 JAN 16 1704 52.38 36 50.20 121 34.53  7.81 74   .21  .3  .6 SJB   2.5
93 JAN 16 1706 16.72 36 50.12 121 34.51  7.83 63   .20  .3  .6 SJB   2.3
93 JAN 16 1909 13.83 39 22.58 122 52.46  5.83 30   .17  .4 1.7 BAR   2.7

93 JAN 17  137 34.28 38 46.59 122 45.19  0.07 16   .06  .2  .7 GEY * 2.3
93 JAN 17  137 46.47 40 22.50 122  5.67 14.36  7   .08  .8 3.3 SHA   2.8
93 JAN 17  300 26.36 39 57.06 120 48.33  0.96 29   .16 1.111.3 WAK - 3.2
93 JAN 17  558  4.29 36 49.84 121 34.01  7.59 62   .22  .3  .7 SJB   2.2
93 JAN 17 1115  7.82 38 49.04 122 46.01  3.04 22   .11  .3  .7 GEY   2.4

93 JAN 17 1541 48.17 36 50.12 121 34.66  8.52 80   .20  .3  .5 SJB   2.9
93 JAN 17 1716 57.99 36 49.97 121 34.19  7.91 57   .23  .4  .6 SJB   2.3
93 JAN 17 1731 53.42 38 50.30 122 49.18  2.83 17   .09  .3  .9 GEY   2.2
93 JAN 17 1752  0.68 36 49.84 121 34.05  7.47 63   .21  .3  .6 SJB   2.6
93 JAN 17 2204 39.35 40 23.43 122  6.21 11.28 16   .22  .6 3.3 SHA   2.3

93 JAN 18  112 52.73 38 50.91 123  0.22  3.88 12   .10  .4 3.1 MAA   2.2
93 JAN 18  320  4.80 40 27.85 124 29.79 17.09 10   .06 2.5  .4 MEN   3.0
93 JAN 18  935 46.03 39 42.71 123 31.28  7.85 10   .08  .7 1.1 MAA   2.0
93 JAN 18 1629 59.24 36 10.50 118  1.93  2.03 11   .06  .8 2.5 OWV   3.1
93 JAN 18 1841 15.68 40  0.50 121 11.13  3.39  9   .06  .9 8.3 ALM - 2.1

93 JAN 18 1856 29.64 39 45.19 123 40.60  4.46 13   .11  .6 1.0 MAA   2.4
93 JAN 18 2327 10.66 38 50.47 122 46.40  3.09 42   .19  .3  .6 GEY   3.6
93 JAN 19   24 29.22 38 50.70 122 46.59  2.48 46   .19  .2  .8 GEY   3.5
93 JAN 19   32 41.85 38 49.83 122 47.64  2.51  9   .04  .3  .7 GEY   2.2
93 JAN 19 1309  2.32 40 22.43 122  5.24  6.24  7   .05 3.1 8.5 SHA - 2.2

93 JAN 19 1922 40.15 35 42.33 118 26.31  8.49 11   .09  .5 1.4 WWF   2.1
93 JAN 19 2123 43.75 38 49.82 122 47.39  2.24 11   .06  .3  .6 GEY   2.1
93 JAN 20  909 55.11 38 48.19 122 46.90  3.82 11   .18  .6  .7 GEY   2.2
93 JAN 20 1244 57.06 37  2.06 121 29.15  6.40 80   .12  .2  .5 CYS   2.4
93 JAN 20 1318 18.14 40 14.71 124 40.47  9.22 12   .1210.212.9 MEN - 3.2

93 JAN 21  251 36.10 40  2.94 122  8.61  3.30  7   .03 2.7 7.0 KLA - 2.2
    
         
 TABLE 2.
Data from National Earthquake Information Center (NEIC)

UTC TIME    LAT     LONG    DEP GS MAGS  SD STA  REGION AND COMMENTS
HRMNSEC                         MB  Msz     USED
-----------------------------------------------------------------------------
JAN 14
105333.3? 19.46 N  64.52 W  33N 4.4     0.9  16 VIRGIN ISLANDS
143044.6* 23.833N 143.389E  33N 4.8     1.2  39 VOLCANO ISLANDS REGION
170608.9? 36.66 N  98.31 W   5G         1.2   6 OKLAHOMA. mbLg 3.1 (TUL), 3.1
        (GS). Felt at Cherokee, Helena, Jet and Nash.
223455.2* 18.617S 175.159W 158D 4.6     0.5  14 TONGA ISLANDS

JAN 15
020250.5  35.038N  85.008W   5G         0.9  13 TENNESSEE. mbLg 3.1 (GS). Felt
        in the Chattanooga-Cleveland area and at Etowah. Also felt in northern
        Georgia.
110600.7  43.017N 144.201E 100G 5.9     0.9 191 HOKKAIDO, JAPAN  REGION.
                                                Foreshock.
110606.3  43.040N 144.108E 100G 6.9     0.8  48 HOKKAIDO, JAPAN  REGION.
        Mo=5.5*10**20 Nm (PPT). One person killed, at least 364 people injured
        and damage (VI JMA) at Kushiro, Hokkaido and Hachinohe, Honshu. Felt (V
        JMA) at Obihiro and Urakawa; (IV JMA) at Hakodate, Otaru and Tomakomai;
        (III JMA) at Sapporo, Hokkaido. Also felt (IV JMA) at Aomori and
        Morioka; (III JMA) at Akita, Fukushima, Sendai, Tokyo and Yokohama,
141757.4  39.215N 116.351W  10G 4.2     0.6  27 NEVADA

JAN 16
062933.5  36.940N 121.581W  10G 4.8     0.8  33 CENTRAL CALIFORNIA. MD 5.1 (GM).
        area from Monterey to Santa Rosa.
105506.3* 20.688S 179.036W 600G 4.6     0.9  23 FIJI ISLANDS REGION

JAN 17
053606.8* 19.612S 168.785E  33N 5.1     1.2  16 VANUATU ISLANDS
084748.0  42.150N 125.955W  10G 4.0     0.6  28 OFF COAST OF OREGON
102532.1  64.946N 149.403W  10G 4.3     0.8  19 CENTRAL ALASKA. ML 4.7 (AEIC).
                                                Felt at Fairbanks.
105123.6  43.586N  12.269E  10G         1.0  27 CENTRAL ITALY. ML 4.2 (VIE), 3.7
134936.1? 11.73 N  87.18 W  33N 4.9     1.1  42 NEAR COAST OF NICARAGUA

JAN 18
011808.8  18.420N 145.887E 168D 5.8     0.8  69 MARIANA ISLANDS
093032.0  34.591N 116.578W   5G         0.5  14 SOUTHERN CALIFORNIA. ML 3.2
115532.0  34.597N 116.642W   5G         0.9  13 SOUTHERN CALIFORNIA. ML 3.3
124208.0  30.800N  90.220E  33N 5.7 5.7 0.8  48 XIJANG. Felt at Lhasa.
232710.2  38.829N 122.781W   5G         1.0  20 NORTHERN CALIFORNIA. ML 4.0

JAN 19
002429.2  38.831N 122.736W   5G         0.8  19 NORTHERN CALIFORNIA. ML 3.6
143927  Q 38.7  N 133.5  E 460  6.0     0.9 118 SEA OF JAPAN
230611  Q  1.2  N 126.1  E  33N 5.7     0.7  34 NORTHERN MOLUCCA SEA

JAN 20
023056  Q  3.1  N  97.7  E  80  6.2     0.9 120 NORTHERN SUMATERA, INDONESIA
173115  Q  7.1  S 128.8  E  33N     6.3 0.8  41 BANDA SEA


Notes: Origin time in the list is in GMT, in the text and on maps
       it is in local time.
       N RD: is the number of readings used to locate the event.
       N S: is the number of S waves in N RD.
       RMS SEC: is the root mean squared residual misfit for the
                location is seconds, the lower the better, over 0.3
                to 0.5 seconds is getting bad, but this is machine,
                not hand timed, data.
       ERH: is the estimated horizontal error in kilometers.
       ERZ: is the estimated vertical error in kilometers.
       N FM: is the number of readings used to compute the magnitude.
       REMKS: obtuse region codes that denote the velocity model
              used to locate the event.
       DUR MAG: is the magnitude as determined from the duration of
                the seismograms, not the amplitude.  Sort of like
                going to echo canyon and measuring how loud your
                yell is by counting echos.
       FIG: denotes the figure/event number in the maps posted separately.
Newsgroups: sci.geo.geology