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
   August 27 - September 2, 1992

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   
   
    For the 7-day period ending at midnight on Wednesday, September 2,
1992 the U.S. Geological Survey office in Menlo Park recorded 24
earthquakes of magnitude one (M1) and greater within the San Francisco Bay
area shown in Figure 1.  Five of these were as large as M2.0.  The weekly
total compares with 22 earthquakes recorded during the previous 7-day
period, only one of which was as large as M2.0. 
    Three of the five M2 events recorded during the week occurred along
the San Andreas system; interestingly, all three occurred within an 8-hour
period last Sunday.  On the peninsula a M2.5 earthquake occurred Sunday
morning about 3 miles offshore of Pacifica along one of the splay faults
to the San Andreas (#3/1).  The Loma Prieta segment experienced a couple
of small earthquakes, the largest a M2.0 Sunday afternoon that occurred at
it's southern end, about 4 miles northeast of Watsonville (#4/1). The
creeping segment of the San Andreas also experienced several small events,
capped by a M2.1 event Sunday evening 2 miles southwest of San Juan
Bautista (#5/1).  
   Activity was also observed on numerous faults in the East Bay.  The
central Calaveras produced several small earthquakes, the largest a M2.2
event about 9 miles east of San Jose (#7/1).  The Mission fault
experienced a M1.9 event early Monday morning (#6/1).  The Hayward fault
saw two M1 events: a M1.7 last Thursday about 4 miles northeast of San
Leandro (#1/1) and a M1.1 early Sunday morning 3 miles northwest of
Fremont.  At the north end of the Calaveras, near the "step over" to the
Concord fault, a M1.9 occurred Tuesday afternoon (#9/1).  Monday evening a
M1.8 occurred near the Antioch fault about 9 miles northwest of Antioch
(#8/1).  Finally, a M2.1 event occurred last Thursday in the northern
Diablo Range about 12 miles east-southeast of Livermore (#2/1).   

Northern California
    
    There was a noticeable increase in seismicity in northern California
during the past week, both in the number of earthquakes larger than M2 and
in the number of M3 earthquakes. Three M3 earthquakes occurred along the
Mendocino transform fault alone, the most in one week in the Cape
Mendocino area since mid-July (#3,#4/2).  The only other earthquake of
note in this area was a M2.1 event 42 miles northeast of Eureka.  The
focal depth calculated for this earthquake was 35 km, placing this
earthquake below the North American plate, either within the underlying
Gorda Plate, or along the interface between the two plates.    
   
    South of Cape Mendocino, a M2.0 earthquake occurred Saturday evening
along the San Andreas near Point Arena (#5/2).  Although the San Andreas
is generally believed to be "locked" between the Golden Gate and Cape
Mendocino, occasional small earthquakes have been observed in this area in
the past 30 years, some as large as M3.  The most recent activity near
Point Arena was a pair of M2 events in April of 1991.
    East of Point Arena, a handful of M2-3 earthquakes occurred in the
central Coast Ranges south and west of Clear Lake.  Just after midnight
Friday a M2.1 occurred west of the Maacama fault, about 12 miles south of
Ukiah.  Wednesday morning a pair of M2 earthquakes occurred only a minute
apart near the southeast end of Clear Lake, about 17 miles east of
Lakeport (#7/2).  Finally, Wednesday afternoon a M3.0 earthquake occurred
in the Geysers geothermal area (#9/2), the largest earthquake seen here
since a M3.1 in mid-June of this year.
     In the eastern Sierra Nevada the Mono Basin was once again active,
producing 7 earthquakes as large as M2, the largest a M3.0 event last
Thursday evening that initiated the sequence (#2/2).  This activity
occurred in the east end of the basin, the same location as the
"triggered" earthquakes that followed the M7.5 Landers earthquake in late
June.  The area had been quiet at the M2 level since early August. 
     To the north, a number of M2 earthquakes occurred in the vicinity of
Lake Tahoe including a M2.6 last Thursday that was located directly
beneath the lake itself (#1/2).  Sunday evening a M3.2 occurred about 6
miles northwest of Truckee (#6/2).

Long Valley Caldera
        
     Activity also increased noticeably in the Long Valley caldera over
that observed during the previous few weeks.  A small swarm occurred early
in the week in the south moat area, about 1 mile southeast of Mammoth
Lakes. It consisted of six M2 events that occurred within an eight-hour
period last Friday night (#1/3).   The area remained quiet until Tuesday
morning when a M2.1 occurred along the southern edge of the caldera 5
miles southeast of Mammoth Lakes (#2/3).  
     Activity south of the caldera was limited with only two M2
earthquakes, both late Wednesday.  The first, a M2.4, occurred about one
mile northwest of Mt. Morrison (#3/3); the second, a M2.0, occurred
beneath Wheeler Crest, near Round Valley Peak (#4/3).     
     

USA Seismicity
    
   For the second week in a row the National Earthquake Information
Service reported a M5.5 in the lower 48 states.  But, whereas last week's
earthquake occurred offshore of southern Oregon and was barely felt, this
week's earthquake occurred in southwestern Utah, produced some damage, and
was felt strongly over a wide area (#4/4).  The moderate earthquake,
occurring early Wednesday morning, produced some damage in the town of
Hurricane, Utah and was felt as far away as Las Vegas, Nevada.  Rock falls
caused by the earthquake closed some roads, including the main road
through Zion National Park, which had to close temporarily as a result. 
     Last Friday a M3.9 occurred in eastern Idaho, about 40 miles
northeast of Borah Peak (#1/4).  It was felt in Arco, Idaho and as far
away as Butte, Montana.  Sunday evening, a M3.6 occurred in north central
Wyoming (#2/4).  
     In southern California aftershocks to the M7.5 Landers earthquake
continue to decline.  During the past week, only 7 aftershocks as large as
M3 were recorded, the largest a M4.2 event early Monday that occurred
along the Landers rupture (#3/4).   
   
     
The Planet Earth

    Two deadly earthquakes occurred during the past week according to
information provided by the National Earthquake Information Service.  Last
Friday a M5.7 earthquake struck western Pakistan killing at least three
people in the Kalat area (#1/5).  Then Tuesday afternoon a M7.0 earthquake
struck about 35 miles off the coast of central Nicaragua (#6/5).  Although
the shaking from the earthquake was not strong enough to cause serious
damage, the tsunami waves generated by the earthquake caused devastation
along several hundred miles of the Nicaraguan coast.  At least 62 people
were reported killed, 227 injured, and approximately 3,000 were still
missing from the waves that were estimated to have been as high as 25 feet
and that had run-ups of up to 1000 meters in places.   Some damage was
also reported in Costa Rica.  The earthquake was felt throughout most of
Nicaragua and as far south as San Jose, Costa Rica.  Seven M5 aftershocks
occurred in the 18 hours following the mainshock.
    Earlier in the week, an earthquake of nearly the same magnitude
occurred along the mid-Atlantic Ridge, north of Ascension Island (#2/5).  
Two M6.0 earthquakes occurred along the western Pacific margin, the first
last Friday offshore the southeast coast of Honshu, Japan (#3/5), the
second on Tuesday beneath the island of Taiwan (#5/5).  A M5.1 occurred
in the Gobi Desert of southeast Mongolia on Monday (#4/5).     

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 AUG 27 1355  3.26 38 40.81 119 38.80  0.06 12 1 .07 1.0 1.3 WAK   2.4
92 AUG 27 2025 15.79 39  6.97 120  1.63 11.12 29 1 .16 1.2 4.0 WAK   2.9
92 AUG 27 2220 49.43 38 44.60 122 42.45  2.79 17   .06  .2  .8 NAP   2.1
92 AUG 28  229 57.44 38  1.34 118 43.75  7.72 26   .16 1.0 5.4 MOL   3.0
92 AUG 28  456 28.90 37 39.03 118 56.35  6.58 19   .12  .4  .7 SMO   2.1
92 AUG 28  457  6.12 37 38.64 118 56.96  6.43 32   .12  .3  .4 SMO   2.9
92 AUG 28  559 17.92 38  1.10 118 43.74  6.81 30   .11  .7 5.6 MOL   2.8
92 AUG 28  634 11.41 37 38.72 118 56.66  6.47 41   .14  .3  .4 SMO   2.1
92 AUG 28  636 34.34 37 38.60 118 56.90  6.45 37   .14  .3  .5 SMO   2.2
92 AUG 28  738 44.75 37 38.70 118 56.79  6.73 40   .13  .3  .4 SMO   2.5
92 AUG 28 1117 52.92 38  1.58 118 43.57  8.40 39   .10  .9 3.2 MOL   2.3
92 AUG 28 1244 43.33 37 38.66 118 56.88  6.63 42 1 .13  .3  .4 SMO   2.7
92 AUG 28 1504 12.31 40 20.02 125 11.07  5.73 19   .25 3.915.1 MEN   2.3
92 AUG 28 1745  7.56 40 17.29 124 21.38  6.96 24 1 .16  .7  .3 MEN   2.7
92 AUG 28 2103 49.48 40 20.77 125  9.05  1.07 25   .20 3.7 6.1 MEN   3.0
92 AUG 29  155 39.19 37 35.03 121 34.78  1.54 50 2 .17  .4 2.3 HAM   2.2
92 AUG 29  248 22.69 38 47.16 122 46.24  3.22 22   .09  .3  .7 GEY   2.3
92 AUG 29  710 41.16 38 58.62 123 10.61  5.75 19   .08  .3 1.7 MAA   2.1
92 AUG 29  756 50.83 39 36.71 119 56.65  6.83 14 1 .18 2.1 2.4 WAK   2.2
92 AUG 29 1111 53.99 40 21.20 125  4.36  9.23 18   .16 4.1 3.2 MEN   2.2
92 AUG 29 1616 35.14 41  1.47 123 25.64 35.15 23 2 .14  .4 1.2 KLA   2.3
92 AUG 29 1843 58.18 38  1.91 118 43.54  7.59 40 1 .11  .9 4.7 MOL-  2.5
92 AUG 29 1933 45.99 40 17.43 124 22.24 14.21 22 1 .14  .6  .3 MEN   2.5
92 AUG 29 2317 35.26 38  2.31 118 43.40  7.22 33 1 .13 1.2 7.3 MOL-  2.3
92 AUG 30  227  7.17 38 51.80 123 41.10  2.58 18 1 .15 1.1 2.0 PAR   2.0
92 AUG 30 1049 12.97 38 48.63 122 48.45  4.60 41   .16  .3  .5 GEY   2.1
92 AUG 30 1517 58.84 39 40.77 120 22.06 14.96 30 1 .13 1.2 3.1 WAK   2.8
92 AUG 30 1623 27.71 37 38.30 122 31.85  0.63 84   .22  .3 1.9 SFP   2.5
92 AUG 30 1721 42.02 36 56.38 121 41.08 12.24 67 1 .12  .2  .4 SJB   2.0
92 AUG 30 1745  7.58 40 17.44 124 21.35  7.31 12   .09  .7  .3 MEN   2.8
92 AUG 30 2342  9.19 39 24.08 120 14.38 15.70 35 1 .17 1.4 2.0 WAK   3.3
92 AUG 31    9 50.23 36 49.71 121 33.56  7.01 52   .20  .3  .6 SJB   2.1
92 AUG 31   39 17.02 40 16.10 124 27.63 30.62 20 1 .12  .8  .6 MEN   2.4
92 AUG 31 1833 49.96 37 22.04 121 43.81  5.88 21   .06  .3  .5 ALU   2.2
92 AUG 31 2303 11.02 36 31.11 121  5.96 10.60 38 3 .08  .2  .5 PIN   2.2
92 SEP  1 1721 56.74 37 37.22 118 53.47  9.87 17   .10  .4  .6 SMO   2.0
92 SEP  1 2058  3.25 36 28.46 121  2.46  1.43 22   .07  .2 1.0 BIT   2.1
92 SEP  2  409 51.16 40 28.81 124 28.37 26.48 21 2 .09  .8  .6 MEN   2.2
92 SEP  2  735 25.20 40 18.46 124 25.33  7.92 25 2 .13  .7  .3 MEN   3.4
92 SEP  2  736 41.36 40 18.38 124 25.18  8.31 26 2 .14  .8  .4 MEN   3.3
92 SEP  2  740 46.68 40 18.49 124 25.21  8.04 19 1 .09  .7  .4 MEN   2.0
92 SEP  2 1755 45.78 38  0.28 118 43.94  7.51  9   .09 1.9 5.6 MOL   2.0
92 SEP  2 1759 57.28 39  0.87 122 35.77  3.69 23   .20  .5 1.7 BAR   2.6
92 SEP  2 1800 54.69 39  1.21 122 35.38  0.10 20   .24  .5 3.6 BAR * 2.4
92 SEP  2 1839 36.23 36 43.92 121  1.06  1.16 70   .27  .4 4.1 ORT * 2.6
92 SEP  2 1918 23.17 39 32.61 121 10.07  9.25 15   .07  .5 1.4 WAK   2.4
92 SEP  2 1934 59.97 40 23.01 124 13.22  9.61 11   .08  .4  .6 MEN   2.1
92 SEP  2 2040 26.72 38 50.04 122 48.41  0.04 35   .25  .4 1.3 GEY * 3.0
92 SEP  2 2102 53.85 37 34.19 118 52.46  6.02 16   .09  .4  .8 MOR   2.4
92 SEP  2 2142 53.79 38 48.82 122 46.48  2.54 15   .12  .4  .7 GEY   2.0
92 SEP  2 2204 18.47 40 28.24 124 41.87 30.30  8   .09 4.9 2.3 MEN   2.2
92 SEP  2 2303 23.45 37 58.76 118 41.08  4.96 14   .08 1.4 2.7 MOL   2.0
92 SEP  3  302 43.97 37 27.09 118 41.20  5.28 26   .08  .4 1.5 WCS   2.0

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.
Data from National Earthquake Information Center (NEIC)

UTC TIME    LAT     LONG    DEP GS MAGS  SD STA  REGION AND COMMENTS
HRMNSEC                         MB  Msz     USED
---------------------------------------------------------------------------
AUG 27
081136.7* 17.603N 101.336W  33N 4.2     0.8  22 NEAR COAST OF GUERRERO, MEXICO
122856.9  38.669N 142.236E  45  4.6     1.0  26 NEAR EAST COAST OF HONSHU, JAPAN
153714.3* 54.506N 166.459E  33N 4.4     0.6  27 KOMANDORSKY ISLANDS REGION
162816.4* 54.455N 166.473E  33N 4.4     1.1  20 KOMANDORSKY ISLANDS REGION
180412.9?  9.70 N 126.52 E 150? 4.2     1.7  11 MINDANAO, PHILIPPINE ISLANDS
AUG 28
005054.2  29.130N  66.792E  33N 5.7 5.6 1.1  59 PAKISTAN. At least three people
        killed in the Kalat area. Felt at Khuzdar, Manguchar, Mastung & Quetta
084041.9* 23.599S 179.052E 550G 4.6     0.8  38 SOUTH OF FIJI ISLANDS
095124.1* 12.394N  89.479W  24D 5.1 4.2 0.9  63 OFF COAST OF CENTRAL AMERICA
152616.3  44.578N 113.336W   5G         0.8  37 EASTERN IDAHO. ML 3.9 (GS). Felt
        at Arco. Felt slightly at Butte, Montana.
171506.3* 22.016S 179.621W 596D 5.0     0.9  50 SOUTH OF FIJI ISLANDS
181845.6   0.906S  13.658W  10G 6.5 6.9 1.0 131 NORTH OF ASCENSION ISLAND.
AUG 29
131037.8  54.442N 166.508E  37D 5.0 4.8 0.9  68 KOMANDORSKY ISLANDS REGION
132002.7  54.458N 166.515E  33N 4.7     0.8  34 KOMANDORSKY ISLANDS REGION
150905.9  54.578N 166.431E  33N 4.6 4.1 1.0  37 KOMANDORSKY ISLANDS REGION
191907.3  33.227N 137.990E 307D 6.0     0.7 123 NEAR S. COAST OF HONSHU, JAPAN.
204559.8  60.782N 151.066W  78*         1.1  15 KENAI PENINSULA, ALASKA
AUG 30
030814.1  58.424N 151.422W  33N         1.1  17 KODIAK ISLAND REGION. ML 4.3
073228.8* 54.681N 166.357E  33N 4.4     0.6  17 KOMANDORSKY ISLANDS REGION
081512.0  33.999N 118.375W  14          0.7  35 SOUTHERN CALIFORNIA. ML 3.3
        (GS). Felt in the Los Angeles area.
112521.4* 15.154S 173.720W  48D 5.0 5.1 0.6  28 TONGA ISLANDS
135113.3  64.829N 165.684W  18D 4.4     1.0  37 NORTHERN ALASKA. ML 4.7 (AEIC).
                                                Felt at Nome.
200907.5  17.586S 178.765W 574D 5.9     0.8 101 FIJI ISLANDS REGION.
AUG 31
014014.7* 43.776N 107.028W   5G         0.8  10 WYOMING. ML 3.6 (GS).
043956.1* 11.394S 118.259E  33N 5.4 4.7 1.5  19 SOUTH OF SUMBAWA, INDONESIA
054436.0* 54.663N 166.280E  33N 4.5     0.8  22 KOMANDORSKY ISLANDS REGION
072554.3  43.903N 106.956E  33N 5.1 4.8 0.9  49 MONGOLIA
092538.1  34.474N 116.445W   5G         0.8  17 SOUTHERN CALIFORNIA. MD 4.2
161910.0  27.222N 142.538E  33N 4.8     0.7  32 BONIN ISLANDS REGION
194223.1* 20.800N  94.446W  10G 4.2     1.1  20 BAY OF CAMPECHE
SEP 01
121723.8  34.587N 116.359W   5G         0.9  20 SOUTHERN CALIFORNIA. MD 3.7
164111.1  23.746N 121.506E  33N 6.0 5.4 0.8  51 TAIWAN
211757.0  34.244N 116.765W   5G         0.8   9 SOUTHERN CALIFORNIA. MD 2.9
SEP 02
001600.9  11.808N  87.354W  33N 5.4 7.0 1.1  75 NEAR COAST OF NICARAGUA.
        Mo=3.2*10**20 Nm (PPT). At least 62 people killed, 227 injured and 3,000
        missing in Nicaragua. At least 600 houses destroyed along the west coast
        of Nicaragua. Some damage also reported in Costa Rica. Most of the
        casualties and damage are believed to be caused by a tsunami affecting
        the west coasts of Nicaragua and Costa Rica, reaching heights up to 8
        meters. Tsunami run-up of 1000 meters was reported at Masachapa, where
        at least 15 people were killed. Felt in Chinandega and Leon Departments,
        Nicaragua. Also felt at El Crucero, Managua and San Marcos, Nicaragua
        and at San Jose, Costa Rica.
002103.7* 10.529N  87.207W  33N 5.7     0.9  52 OFF COAST OF COSTA RICA
002827.9? 11.64 N  87.49 W  33N 5.2     1.0  22 NEAR COAST OF NICARAGUA
003101.2? 11.70 N  88.16 W  33N 5.4     1.0  28 OFF COAST OF CENTRAL AMERICA
005733.8* 11.063N  87.595W  33N 5.3     0.9  51 NEAR COAST OF NICARAGUA
014241.3* 11.695N  87.920W  33N 5.4     1.0  64 NEAR COAST OF NICARAGUA
055002.7*  5.943S 112.266E 635D 5.9     0.7  21 JAVA SEA
102619  Q 37.0  N 113.5  W  10G 5.5     0.8  54 UTAH
165045  Q 10.1  N  86.5  W  33N 5.5     1.0  62 OFF COAST OF COSTA RICA
182857  Q 11.0  N  86.8  W  33N     5.5 1.2  67 OFF COAST OF COSTA RICA