From: andy@pangea.Stanford.EDU (Andy Michael USGS Guest)
Subject: N. CA, USA, and World Quake Report 4/2-8/92
Organization: Stanford Univ. Earth Sciences
Date: Fri, 10 Apr 1992 17:25:04 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 2 - 8, 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 was low during the past week throughout the Bay Area and
in much of northern and central California.  For the 7-day period ending at
midnight on Wednesday, April 8, 1992 the U.S. Geological Survey office in
Menlo Park recorded 15 earthquakes of magnitude one (M1) and greater
within the San Francisco Bay area shown in Figure 1.  Only two of these
were as large as M2.0.  This compares with 28 earthquakes recorded during
the previous 7-day period,  eight of which were as large as M2.0. 
    The largest earthquake in the area during the week was a M2.2 in the
East Bay, about 11 miles southeast of Antioch (#2/1).  This event was near
the southern end of the Antioch fault.  
    The only other earthquakes of any note were a pair of M1 events along
the Hayward fault and a M1 on the northern Peninsula segment of the San
Andreas.  The first Hayward event occurred early last Friday afternoon and
was located about 3 miles southeast of Berkeley (#1 in figure 1).  This is
the same location as a pair of M2 earthquakes that had occurred during the
previous week.  The second Hayward event occurred Wednesday evening about
2 miles southeast of Hayward (#5/1).  This was about 5 miles southeast of
a pair of M1 events that occurred during the previous week.  The Peninsula
earthquake occurred early Monday morning approximately 1 mile south-
southeast of Pacifica (#3/1).  It occurred on one of the numerous small
splay faults of the San Andreas that criss-cross this area northeast of
Montara Mountain.
     
Northern California
    
    Seismicity remained low throughout most of northern California during
the past 7 days.  Only three M2 events occurred in the Cape Mendocino area,
similar to the level of activity observed here during the previous week. 
Two of these events occurred last Thursday along the Mendocino escarpment,
the westward extension of the San Andreas system that is typically one of
the most seismically active areas on the west coast (#1/2).  The third
event occurred early Monday morning just offshore of Cape Mendocino, about
18 miles southwest of Eureka.
   The most active area during the past week was in the California-Nevada
border region (#2/2).  On Sunday a pair of M2.8 earthquakes and a M4.1
event occurred about 25 miles north-northeast of Truckee and 10 miles
north-northwest of Reno, NV.  The M4.1 event was the largest earthquake
recorded during the week and was widely felt in the Reno area. 
  
   Activity in central California was limited to the creeping section of
the San Andreas with a pair of M2 events early Tuesday morning about 23
miles southeast of Hollister (#3/2), a M3.4 event later the same day about
17 miles east of King City (#5/2), and a M2.2 event Wednesday morning at
the southern end of the creeping segment, about 12 miles northwest of
Parkfield (#6/2).  
  
Long Valley Caldera

    Three earthquakes in the Long Valley area  were as large as M2.0.  All
were located near the southern boundary of the caldera and west of the
Hilton Creek fault.  The first of these was a M2.2 event Monday morning
about 2 miles southwest of McGee Mountain (#2/3).  Later that day a M2.1
occurred just inside the caldera about 1 mile northeast of Convict Lake
(#3/3).  The next day a M2.0 event occurred just east of the north end of
Convict Lake (#4/3).  No activity was recorded in the south moat or
resurgent dome area of the caldera.  

USA Seismicity

   If seismicity was slight in California it was increased in other regions
of the country, at least according to data from the National Earthquake
Information Center which is charged with monitoring seismicity in the
United States and throughout the world.  Utah experienced three notable
earthquakes during the week--a M3.0 and a M2.5 last Thursday beneath the
northern Great Salt Lake (#1/4) and a M3.3 Monday evening about 15 miles
east of Richfield (#5/4).  A M4.1 earthquake occurred last Friday afternoon
along the Idaho/Wyoming border, about 35 miles east of Rexburg, Idaho and
just west of the Grand Teton National Park (#3/4).  A slightly larger M4.3
earthquake occurred later the same day off the coast of central Oregon at
roughly the latitude of Tilamook Head (#4/4).  The only notable earthquake
east of the Mississippi (and this by less than 20 miles) was a M3.5 event
located just north of Ripley, Tennessee that was felt in Dyer and
Lauderdale counties (#2/4).      

The Planet Earth

    Seismicity appears to have increased worldwide as well with numerous M5
and M6 events along the Pacific margins.  While the Aleutian chain was
essentially quiet during the week, M4 and M5 earthquakes were observed
along the western rim of the Pacific from Kamchatka to the central
Philippines.  The southwest Pacific produced several M6 events including a
M6.6 in the New Britain Region of Papua New Guinea (#2/5) and a pair of
M6.0 events in the Santa Cruz and Vanuatu Islands (#4/5).  
    Along the eastern Pacific rim notable earthquakes included:  a M5.5
beneath the Chile-Argentina border region (#3/5), a M5.5 off the coast of
Costa Rica (#5/5), and a number of moderate earthquakes in the Vancouver
Island Region, the largest a M6.6 event (#6/5).    

              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

92 APR  2 1917 37.04 40 17.44 124 21.64 10.48 11   .10 1.1  .6 MEN   2.3
92 APR  2 2236 19.86 40 18.65 124 42.63  5.00 10   .3610.1 9.9 MEN   2.8
92 APR  3 2141  3.93 38 49.15 122 50.06  0.06 11   .10  .3 1.0 GEY * 2.1
92 APR  4 1359 51.98 37 51.86 121 45.65 17.61 35   .13  .6  .3 GRN   2.2
92 APR  5 1058 20.96 38 49.99 122 49.03  0.77 30   .32  .6 6.8 GEY * 2.6

92 APR  5 1059 43.29 38 49.45 122 47.83  0.19 21   .10  .2 1.2 GEY   2.0
92 APR  6  240 52.60 38 24.94 118 24.18  4.26 22   .18 3.216.4 NEV - 2.9
92 APR  6  259 14.40 39 35.01 120  8.41  5.19 11   .24 9.115.3 WAK - 2.8
92 APR  6  328 22.01 39 37.66 120  1.79  0.08 18   .24 2.7 3.3 WAK * 2.8
92 APR  6  401 30.15 39 39.16 119 54.08  4.94 30   .19 2.1 3.3 WAK   4.1

92 APR  6 1153 37.56 40 34.85 124 23.76 23.44  9   .08 1.2 1.0 EUR   2.2
92 APR  6 1154 52.63 36 50.27 121 34.72  7.89 55   .22  .4  .6 SJB   2.0
92 APR  6 1214 17.98 37 33.29 118 49.89  7.14 21   .10  .3  .8 MOR   2.2
92 APR  6 1810  2.01 37 36.47 118 50.01  7.62 15   .08  .3  .5 SMO   2.1
92 APR  7  238 32.14 39 38.55 120  2.53  2.12 16   .44 5.810.0 WAK * 2.6

92 APR  7  638 35.26 38 48.23 122 46.23  2.03 24   .16  .3  .7 GEY   2.1
92 APR  7  807 52.87 36 34.81 121 10.24  4.52 76   .10  .2  .3 PIN   2.5
92 APR  7 1019 42.54 36 34.46 121 10.00  5.19 41   .06  .2  .5 PIN   2.1
92 APR  7 1404 51.67 40 34.15 122 18.24 27.89  9   .15  .7 2.2 SHA   2.4
92 APR  7 1910 34.32 36 14.73 120 49.64  6.51 97   .46  .5 1.1 BIT   3.4

92 APR  7 2252 12.39 37 35.66 118 50.63 10.80 22   .09  .3  .6 MOR   2.0
92 APR  8 1533  3.33 36  2.03 120 34.95  5.17 40   .15  .3  .5 SLA   2.2

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 02
005624.2  63.187N 149.839W 104          0.8  67 CENTRAL ALASKA
013940.4  24.018N 121.802E  33N 4.9 4.3 1.2  30 TAIWAN
031755.9* 37.352S  17.277W  10G 5.3 5.3 1.0  23 SOUTHERN MID-ATLANTIC RIDGE
060322.7* 35.660N 140.715E  33N         0.7  12 NEAR EAST COAST OF HONSHU, JAPAN
064023.2  49.370N 128.724W  10G 4.2     0.9  35 VANCOUVER ISLAND REGION
093329.2  41.409N 112.808W  10G         0.8   9 UTAH. ML 3.0 (GS).
100845.1* 24.697S 179.661E 498D 4.3     0.8  21 SOUTH OF FIJI ISLANDS
102256.4* 41.401N 112.841W  10G         0.9   5 UTAH. ML 2.5 (GS).
102959.9? 32.93 S  72.29 W  10G         0.5  10 OFF COAST OF CENTRAL CHILE. MD
                                                4.0 (SAN).
131231.8  37.502N 141.131E  72D 4.2     1.5  25 NEAR EAST COAST OF HONSHU, JAPAN
135428.2   1.834N 127.616E 118D 5.1     1.1  25 HALMAHERA, INDONESIA
153950.0* 33.700S  72.079W  10G         0.7  10 OFF COAST OF CENTRAL CHILE
185610.5  21.712N 142.710E 320* 4.5     0.7  23 MARIANA ISLANDS REGION
210304.2*  7.278N  34.053W  10G 5.1 5.0 1.1  61 CENTRAL MID-ATLANTIC RIDGE
APR 03
005602.1  61.490N 146.765W  33N 3.7     1.1  12 SOUTHERN ALASKA. ML 3.0 (PMR).
030603.4  35.811N  89.475W   5G         0.6  29 TENNESSEE. mbLg 3.5 (GS). Felt
                                                in Dyer and Lauderdale Counties.
031952.9   5.576S 151.138E  33N 5.8 6.6 0.9  86 NEW BRITAIN REGION, P.N.G.
 060737.8  29.012S  69.399W 109D 5.5     1.1  67 CHILE-ARGENTINA BORDER REGION.
                                                Felt (IV) at Copiapo and
                                                Vallenar, Chile.
APR 04
011113.0  17.758S 178.482W 575D 5.0     1.0  62 FIJI ISLANDS REGION
013009.5  43.838N 111.083W   5G 4.1     0.6  38 EASTERN IDAHO. ML 4.0 (GS). Felt
        at Ashton, Driggs, Rexburg, St. Anthony, Tetonia and Victor. Also felt
        at Alta and Jackson, Wyoming.
063902.9* 54.032N 161.898E  33N 4.6     1.1  18 NEAR EAST COAST OF KAMCHATKA
094856.5  32.157N 141.285E  33N 5.1     1.1  76 SOUTH OF HONSHU, JAPAN
162317.7* 54.017N 161.764E  33N 5.2     0.7  39 NEAR EAST COAST OF KAMCHATKA
174320.7* 28.169N  88.097E  33N 4.9 4.6 1.1  23 XIJANG
184608.4*  2.026S 128.493E  33N 4.8     0.9  11 CERAM SEA
215122.2* 10.845S 165.876E  68D 5.1     1.0  33 SANTA CRUZ ISLANDS.
                                                Mo=5.0*10**17 Nm (PPT).
222942.2  45.244N 125.534W  10G 4.3     0.9  16 OFF COAST OF OREGON
APR 05
074355.9*  4.515N 126.902E  33N 4.9     1.1  11 TALAUD ISLANDS, INDONESIA
074749.6  35.742N  80.683E  33N 5.3 5.1 0.9  36 KASHMIR-XIJANG BORDER REGION
112856.3  63.276N 150.464W 141* 3.2     0.9  14 CENTRAL ALASKA
114633.8* 11.987S 166.171E  40D 5.0 6.0 1.2  43 SANTA CRUZ ISLANDS.
                                                Mo=3.2*10**18 Nm (PPT).
132506.1  48.571N 156.144E  62D 5.2     0.8  63 EAST OF KURIL ISLANDS
141336.0? 10.67 N  86.50 W  33N 5.3 5.5 1.2  53 OFF COAST OF COSTA RICA. Felt at
                                                Managua, Nicaragua.
APR 06
033502.0* 43.785N 146.282E  33N 5.0     0.9  36 KURIL ISLANDS
040128.4  39.720N 119.759W   5G         0.6  13 NEVADA. ML 4.1 (GS). Felt
                                                throughout the Reno area.
135439.0  50.775N 130.171W  10G 6.0 6.6 1.3 100 VANCOUVER ISLAND REGION.
135751.2  50.601N 130.192W  10G 5.4     1.2  31 VANCOUVER ISLAND REGION
144642.9*  2.007S  97.877E  33D 5.6     0.6  22 SOUTHWEST OF SUMATERA, INDONESIA
151608.7  50.742N 129.837W  10G 5.3 5.9 1.0  50 VANCOUVER ISLAND REGION
153318.8  58.476N  32.023W  10G 4.9     0.8  29 NORTH ATLANTIC OCEAN
154901.3  50.682N 129.688W  10G 4.0     0.6  13 VANCOUVER ISLAND REGION
161533.0  58.576N  32.129W  10G 5.4 5.3 0.8  47 NORTH ATLANTIC OCEAN
APR 07
014357.1& 38.773N 111.815W   1               10 UTAH. <SLC-P>. ML 3.3 (GS).
033705.2?  3.94 S 131.13 E  54D 6.0     0.7  16 IRIAN JAYA REGION, INDONESIA
181226.1  50.614N 129.722W  10G 4.3     1.1  30 VANCOUVER ISLAND REGION
224729.1* 16.608S 167.778E  16D 5.3 6.0 0.8  32 VANUATU ISLANDS
APR 08
030132.9? 15.98 S 168.24 E  33N 5.5 5.7 0.7  43 VANUATU ISLANDS
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