From: andy@pangea.Stanford.EDU (Andy Michael USGS Guest)
Subject: N. CA, USA, and World Quake Report 4/9-15/92
Organization: Stanford Univ. Earth Sciences
Date: Fri, 17 Apr 1992 00:42:09 GMT

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
                             April 9 - 15, 1992
                                     
                         Data and text prepared by
     Steve Walter, Nan Macgregor-Scott, 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
   
    Seismicity increased somewhat during the past week, due largely to
activity along the southern Calaveras and Quien Sabe faults.  For the
7-day period ending at midnight on Wednesday, April 15, 1992 the U.S.
Geological Survey office in Menlo Park recorded 22 earthquakes of
magnitude one (M1) and greater within the San Francisco Bay area shown in
Figure 1.  Eight of these were as large as M2.0, including two M3 events
on the southern Calaveras and Quien Sabe faults.  This compares with 15
earthquakes recorded during the previous 7-day period, only two of which
were as large as M2.0. 
    The largest earthquake in the area during the week occurred Sunday
morning, a M3.1 event on the northern Quien Sabe fault about 5 miles
northeast of Hollister (#4 in figure 1).  Activity on the Quien Sabe is
not unusual; two M3.4 events have occurred on this fault in the past year,
along with numerous smaller earthquakes.  
    Approximately 24 hours later, a second M3 earthquake occurred nearby,
this time on the southern Calaveras fault, roughly 6 miles north-northwest
of Hollister (#5/1). This is the largest earthquake to occur on this part
of the Calaveras in over a year; in fact the only earthquake as large as
M2 to occur here within the past year was a M2.5 last July.   
    Other activity in the South Bay occurred along the creeping segment of
the San Andreas fault and included a pair of M2 events in the vicinity of
San Juan Bautista (#1/1) and a M2.4 six miles south of Tres Pinos.  
    To the north, two M2.2 earthquakes occurred within minutes of each
other Sunday morning on the southern end of the Black Mountain thrust
fault (#3/1).  This location is in the foothills of the Santa Cruz
Mountains, midway between Cupertino and Saratoga.
    One M2.5 earthquake occurred last Friday afternoon on the northern 
Peninsula almost directly beneath Pacifica (#2/1).  As was the case with
a M1.9 that occurred in this same location during the previous week, this
earthquake occurred along a splay fault to the San Andreas, not on the San
Andreas itself.
    The only activity in the East Bay during the past week was a pair of
small earthquakes on the central Concord fault, both about 3 miles
east-southeast of Concord (#6/1).  The largest of these was a M2.6 event
that occurred Monday afternoon.  No reports were received that either of
these earthquakes was felt.  Similar magnitude earthquakes have occurred
in this same area during the past year, most recently a M2.0 in early
January.
    

     
Northern California
    
   Seismicity was low throughout the rest of northern California during the
past week.  The only earthquake as large as M3 outside of the Bay Area was
a M3.3 event at the Geysers geothermal area, an area that regularly
experiences earthquakes of this magnitude (#3/2).  Cape Mendocino, another
area that experiences regular activity at the M2-3 level, was unusually
quiet this week with no earthquakes recorded as large as M2.  Several M2
earthquakes were recorded in the northern Sierra-Nevada including a M2.3
event last Friday evening about 17 miles southeast of Quincy (#4/2), a M2.0
event on Sunday 21 miles northwest of Susanville (#5/2), and a M2.5 event
on Tuesday about 20 miles west of Lassen Peak (#7/2).  The only other
earthquake in the Sierra-Nevada region, outside of the Long Valley area,
was a M2.3 event last Friday night beneath the northwest shoreline of Mono
Lake (#2/2). 
   Activity was equally sparse in central California with a couple of M2
earthquakes along the central and southern creeping segment of the San
Andreas (#1/2) and a M2.0 event near the Big Sur coast, about 5 miles
northeast of San Simeon (#8/2).  Early Monday morning a M2.3 earthquake
occurred east of San Luis Reservoir, about 10 miles west of Los Banos
(#6/2).  Several M2 earthquakes have been recorded in this same general
area during the past 15 months.  
  
Long Valley Caldera

     Activity picked up slightly within the caldera during the past week.  For
the first time since early February there were M2 earthquakes inside the caldera. 
In this case the activity was centered in the western end of the south moat area,
the location of one of the most active recent swarms that occurred about 13
months ago (#3,4 in fig.3).  This week's activity was minor by comparison, with
only two M2 events on Wednesday morning, the largest a M2.6, and a pair of M1.5
events.    
     Only minor earthquakes occurred south of the caldera, the largest a M2.1
event last Friday in the vicinity of Mount Morrison (#2/3).
   
USA Seismicity

    The National Earthquake Information Service (NEIS) located no significant
earthquakes in the lower 48 states, outside of California, during the past week.  

The Planet Earth

    A moderate earthquake occurred in the southern Netherlands Monday that was
widely felt throughout that region as well as in northwestern Germany and eastern
Belgium (#4/5).  This was the largest earthquake to have occurred in this area in
generations and produced significant injury and damage.   25 people were injured
in Heinsberg, Germany and 20 people were injured in Roermond, Netherlands.   A
number of smaller aftershocks were recorded by a local seismic network in the
days following, including a M3.5 event that was felt in the immediate area of the
mainshock.
    Two moderate earthquakes occurred along the mid-Atlantic ridge earlier in the
week, the largest a M5.2 event (#1/5).  This deep-sea volcanic rift zone, where
new oceanic crust is being created, has experienced a number of similarly-sized
earthquakes during the past year.
    As usual, the western Pacific margin experienced the most earthquakes, though
none this past week were as large as M6.  The most notable events along this
western rim of the "Ring of Fire" include a M5.4 in southern Sumatera, Indonesia
(#3/5), a M5.3 near the east coast of Honshu, Japan (#5/5), and a M5.5 in the
Andreanof Islands of the Aleutian archipelago (#6/5).
  
                 Table 1.  Central California Seismicity (M>2.0)

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

92 APR  9 1558 38.94 36 32.22 121  6.85  2.35 63   .12  .2  .6 PIN   2.6
92 APR 10 1030 50.83 38  3.95 119  5.41 11.10 13   .13 1.0 1.0 MOL   2.3
92 APR 10 1650 34.95 37 28.76 118 51.14  6.58 24   .09  .3 1.0 MOR   2.1
92 APR 10 1727 36.64 38 49.36 122 49.95  0.02 31   .14  .2  .9 GEY   2.4
92 APR 10 2144 24.26 36 53.89 121 37.07  2.40 18   .11  .3  .7 SJB   2.1

92 APR 10 2146 36.74 38 47.35 122 45.25  2.64 14   .13  .4 1.0 GEY   2.0
92 APR 10 2233 49.20 38 47.53 122 46.45  2.20 52   .18  .2  .6 GEY   3.3
92 APR 11  407 35.35 39 43.68 120 46.34  9.46 10   .07 3.5 4.4 WAK   2.3
92 APR 11  420 46.80 37 37.78 122 28.70  4.24 67   .21  .4  .7 SFP   2.5
92 APR 12 1236 56.70 35 30.44 118 18.10 10.89 14   .13  .5 1.4 WWF   2.1

92 APR 12 1318 52.47 37 18.34 122  4.04  2.84 56   .18  .2  .6 BLM   2.2
92 APR 12 1322 53.17 37 18.31 122  3.94  3.79 65   .16  .2  .5 BLM   2.2
92 APR 12 1340 23.38 36 54.29 121 21.09  7.80100   .20  .2  .4 QUI   3.1
92 APR 12 1533 25.99 38 49.54 122 47.28  0.04  8   .10  .3 2.0 GEY * 2.2
92 APR 13   39 23.08 38 51.04 122 47.23  1.71 21   .10  .3  .9 GEY   2.0

92 APR 13  147 40.56 36 14.13 120 47.32  6.58 38   .16  .4  .6 BIT   2.2
92 APR 13  214 47.99 40 30.78 121  1.60  3.72  8   .03 2.9 7.2 MOD - 2.0
92 APR 13  755 43.32 37  5.51 121  1.39  0.42 69   .17  .4 4.6 ORT   2.3
92 APR 13 1135 52.74 36 50.22 121 24.62  8.60 72   .18  .3  .5 HOL   2.2
92 APR 13 1403 48.36 36 56.19 121 26.24  3.17 99   .18  .2  .6 HOL   3.0

92 APR 13 2049 49.65 38 47.60 122 44.74  2.16 22   .18  .3  .8 GEY   2.0
92 APR 13 2120 53.67 38 47.75 122 47.58  0.73 27   .16  .3  .7 GEY   2.2
92 APR 13 2326 29.13 37 58.02 122  1.34 14.53 73   .23  .3  .4 CON   2.6
92 APR 14 1516 48.81 38 47.70 122 45.80  1.51 34   .19  .3 1.7 GEY   2.6
92 APR 14 1707 54.93 40 28.35 121 53.25 17.38 21   .33  .8 2.0 SHA   2.5

92 APR 15  332  9.92 35 41.08 121  7.68  4.04 19   .16  .8 2.0 SSM   2.0
92 APR 15  625 35.78 36 42.18 121 19.96  4.22 72   .15  .2  .5 STN   2.4
92 APR 15 1602  4.80 38 47.12 122 45.22  1.94 19   .16  .3  .9 GEY   2.0
92 APR 15 1650  7.02 36 50.36 121 33.21 11.96 51   .16  .3  .6 SJB   2.0
92 APR 15 2031 55.00 37 37.99 118 57.18  8.59 17   .13  .4  .7 SMO   2.6

92 APR 15 2037 13.44 37 39.47 118 56.55  1.70 14   .18  .4  .4 SMO   2.1
92 APR 16   14 37.45 38 18.75 118 22.08  5.00 10   .1912.517.3 NEV - 3.0

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.

                      Table 2.  Worldwide Seismicity
         Data from the USGS National Earthquake Information Center

UTC TIME    LAT     LONG    DEP GS MAGS  SD STA  REGION AND COMMENTS
HRMNSEC                         MB  Msz     USED
------------------------------------------------------------------------------
APR 09
102157.5  58.992N 152.185W  33N 3.8     1.2  19 KODIAK ISLAND REGION
200246.3  46.837N  27.391W  19D 5.2 4.7 0.9  67 NORTHERN MID-ATLANTIC RIDGE
205337.2  62.354N 148.188W  73?         0.8  13 CENTRAL ALASKA
211430.6  52.497N 160.434E  33N 5.3 4.6 1.0 113 OFF EAST COAST OF KAMCHATKA
231848.4% 33.598S  70.423W 100G         0.3   9 CHILE-ARGENTINA BORDER REGION.
                                                MD 4.0 (SAN).
APR 10
093307.8  33.884S  71.941W  31D 4.7     1.0  32 NEAR COAST OF CENTRAL CHILE
094704.3  60.029N 152.445W 104*         0.4  12 SOUTHERN ALASKA
104038.6? 20.94 S  66.54 W 120? 4.6     0.5  29 SOUTHERN BOLIVIA
114024.0* 11.272S 165.542E  50G 5.0     0.9  16 SANTA CRUZ ISLANDS
143130.7* 35.797N 139.507E  92  4.9     1.0  20 NEAR S. COAST OF HONSHU, JAPAN
161459.4   4.169S 104.668E 228  5.4     0.8  49 SOUTHERN SUMATERA, INDONESIA
201321.3* 33.332N 116.239W   5G         0.9   9 SOUTHERN CALIFORNIA. ML 3.5
APR 11
022130.5* 52.843N  35.036W  20D 4.9 4.4 0.9  17 NORTH ATLANTIC OCEAN
APR 12
134022.5  36.871N 121.414W  10G         0.7  11 CENTRAL CALIFORNIA. ML 3.0
183717.0* 29.825N 131.400E  33N 5.4     0.6  41 SOUTHEAST OF RYUKYU ISLANDS
193608.5  63.106N 150.850W 120  4.2     0.6  15 CENTRAL ALASKA
APR 13
011959.8  51.219N   5.927E  10G 5.4 5.1 0.9  62 THE NETHERLANDS. One person died
        of a heart attack in Bonn, Germany. Twenty-five people were injured in
        Heinsberg, Germany and twenty people were injured in Roermond,
        Netherlands. Damage reported in Koln, Germany and Limburg Province,
        Belgium. Felt strongly in many parts of northwestern Germany, eastern
        Belgium and southern Netherlands.
055845.7  39.008N 142.445E  59D 5.3     0.7  59 NEAR EAST COAST OF HONSHU, JAPAN
140347.2  36.851N 121.586W  10G         0.9   9 CENTRAL CALIFORNIA. ML 2.8 (GS).
171558.2* 51.624N 173.689W  45D 4.4     1.1  25 ANDREANOF ISLANDS, ALEUTIAN IS.
APR 15
053503.1  50.484N 176.011W  33N 5.5 5.0 1.0  70 ANDREANOF ISLANDS, ALEUTIAN IS.
                                                Felt on Adak.