From: andy@pangea.Stanford.EDU (Andy Michael USGS Guest)
Subject: N. CA, USA, and World Quake Report 7/23-29/92
Organization: Stanford Univ. Earth Sciences
Date: Fri, 31 Jul 1992 07:16:00 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
                             July 23 - 29, 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  
             
    For the 7-day period ending at midnight on Wednesday, July 29, 1992
the U.S. Geological Survey office in Menlo Park recorded 20 earthquakes of
magnitude one (M1) and greater within the San Francisco Bay area shown in
Figure 1.  Three of these were as large as M2.0.  This weekly total
compares with 14 earthquakes recorded during the previous 7-day period,
five of which were as large as M2.0. 
    As was the case last week, the larger earthquakes occurred in the
southern part of the Bay Area on the Calaveras fault and on a subsidiary
fault to the San Andreas northwest of Watsonville.  
    The Calaveras events both occurred on Monday afternoon.  The first
event was the largest, a M2.9 located just 1 mile northwest of Hollister
(#2/1).  It was followed just four hours later by a M2.5 event located 6
miles north-northwest of Hollister (#3/1).
    Early last Friday morning a M2.5 event occurred 6 miles west-northwest
of Watsonville (#1/1).  This earthquake was reported to have been felt by
a resident in the immediate area of the epicenter.  A couple of M1
aftershocks followed within the next 24 hours.  This same area was active
about 36 hours after the 1989 Loma Prieta earthquake, producing one of the
two M5 aftershocks that was so destructive to the already damaged
structures in Watsonville.  The Zayante fault is believed to have been
responsible for the M5 aftershock and presumably it was also the source of
the recent small earthquakes.  
    The only other earthquakes worth noting were a M1.6 event southwest of
Antioch last Thursday morning and a M1.1 on the central Concord fault just
before midnight on Wednesday.

Northern California
    
     Seismicity continued at above-normal levels along the eastern margin
of the southern Sierra Nevada during the past week.  This was most clearly
seen in the eastern Mono Basin where activity continued in the M2-3 range
for the fourth straight week (#1/2).  Activity also continued in the White
Mountain region southeast of Mono Lake, another area that "turned on"
following the M7.4 Landers earthquake in late June.  Single M2 earthquakes
were also noted in Chalfant Valley just east of Long Valley caldera, in
the Owens Valley 2 miles southwest of Big Pine (#4/2), and in the southern
Sierra Nevada about 17 miles east of Sequoia National Park (#7/2). 
Activity declined north of Mono Lake and into the southern Cascades.  The
only earthquake as large as M2 in this area was a M2.4 event about 8 miles
south-southeast of Carson City (#5/2).
     In northern California, aftershocks to the M7.0 Cape Mendocino
earthquake of April 28 continued to be recorded (#3/2).  Three aftershocks
occurred last Thursday and Friday that were as large as M3; this compares
to the previous week when the largest aftershock was only a M2.5.  
     A M2.7 earthquake occurred Sunday morning below the central Valley
about 10 miles southwest of Chico (#6/2).  The focal depth of this
earthquake was about 26 km, unusually deep for most earthquakes in
California but similar to depths recorded for two earthquakes that
occurred north of Red Bluff during the previous week.
     Also slightly unusual were a pair of M2 earthquakes that occurred
early last Thursday morning on the Green Valley fault about 6 miles west
of Fairfield (#2/2).  No earthquakes as large as M2 have occurred in this
area in at least the past 18 months, though seismicity maps for the past 2
decades show that occasional earthquakes do occur here, some as large as
M3-4.
    South of the Bay area, half a dozen M2 earthquakes occurred on and
adjacent to the creeping segment of the San Andreas, the most activity
seen here since the week preceding the Landers earthquake.  To the south,
three M2 earthquakes occurred about 11 miles north-northeast of Avenal on
Tuesday evening/Wednesday morning (#8/2).   

Long Valley Caldera
        
    Activity in the caldera increased only slightly during the past week.
Early Tuesday morning one M2.3 earthquake and several M1.5 events occurred
in the south moat area just 3 miles southeast of Mammoth Lakes (#2/3). 
This is the same area that was active the previous week at the M1 level.
    South of the caldera a M2.2 event occurred Saturday near the Round
Valley fault (#3/3) and a M2.2 event occurred Wednesday near Mt. Crocker
(#4/3) 

USA Seismicity
    
    The only activity in the lower 48 states recorded by the National
Earthquake Information Center occurred in California.  Most of this
activity consisted of aftershocks to the M7.4 Landers earthquake (#1/4). 
Two of these aftershocks were as large as M4, both M4.7 events that
occurred last Friday.  The following day a M3.4 earthquake occurred near
the southern end of Death Valley along the Death Valley fault zone (#2/4).
   
The Planet Earth

   Aftershocks to the previous week's M6.9 earthquake offshore Honshu,
Japan continued into this week with a pair of M5 events (#4/5).  A pair of
M5 earthquakes were also recorded off the east coast of Kamchatka (#2/5)
as well as in the New Britain region of Papua New Guinea (#3/5).  A M5.2
quake occurred beneath the Aegean Sea last Thursday (#1/5)and a M5.4 quake
occurred along the mid-Atlantic ridge on Saturday (#5/5).  Finally, three
M4 earthquakes occurred in the Vancouver Island region Wednesday (#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 JUL 23  811 17.96 38  2.97 118 45.64  5.60 27   .12 1.0 7.1 MOL   3.0
92 JUL 23 1316 13.84 38 13.55 122 10.28  9.08 52   .26  .5  .6 GVL   2.6
92 JUL 23 1516 21.59 38 14.07 122  8.47  8.52 27   .24 1.2  .9 GVL   2.3
92 JUL 23 1538 34.79 40 29.98 124 17.63  0.02 15   .19  .9 3.2 EUR * 3.0
92 JUL 23 1836 18.86 36 36.64 120 50.23  0.72 50   .18  .5 4.3 CRV   2.6
92 JUL 23 2211  3.77 40 16.28 124 20.35  8.07 17   .19 1.2  .6 MEN   3.1

92 JUL 23 2307  1.15 36 29.75 121  4.23  0.57 12   .08  .4 2.1 BIT   2.0
92 JUL 24  316 12.75 37 55.61 118 35.26  6.59 12 3 .14 2.3 3.2 MOL   2.0
92 JUL 24  829 59.67 36 57.21 121 50.68  5.42 66   .16  .3  .4 MON   2.5
92 JUL 24 1827 26.99 40 16.71 124 30.36 19.89 13   .08 2.4  .3 MEN   3.0

92 JUL 24 1958 27.74 38 46.88 122 45.98  0.04 15   .11  .3  .9 GEY * 2.0
92 JUL 25  146 27.14 40 18.72 124 21.49  6.80  9   .10 1.1  .5 MEN   2.6
92 JUL 25  906 17.13 37 58.84 118 42.98  7.00 14   .12 2.6 4.2 MOL   2.2
92 JUL 25 1114 20.12 38 11.62 118 50.01  4.72 10   .07 1.5 9.5 MOL - 2.0
92 JUL 25 1353 45.91 36 14.44 120 48.45  9.71 42   .24  .5  .9 BIT   2.2

92 JUL 25 1511 46.75 37  9.07 118 19.37  1.25 11   .2918.710.3 OWV - 2.2
92 JUL 25 1551  2.00 38  2.34 118 48.85  6.29  9   .09 2.510.1 MOL - 2.4
92 JUL 25 2010 50.29 37 28.15 118 36.67 13.65 26   .09  .3 1.0 RVL   2.2
92 JUL 25 2125 32.69 37 34.10 118 28.83 11.61 22   .09  .4  .8 CHV   2.1
92 JUL 25 2208 17.18 39  3.64 119 44.03  0.31 13   .08 3.5 2.0 WAK * 2.4
92 JUL 25 2244 10.23 37 50.75 118 36.82  5.04 10   .06 1.7 1.5 GLA   2.1
92 JUL 26 1223 12.48 38 48.94 122 46.90  1.28 37   .18  .3  .6 GEY   2.5
92 JUL 26 1405 39.40 39 37.85 121 52.88 26.51 25   .12  .4  .9 SAC   2.7
92 JUL 26 1711 43.28 38 29.08 118 12.52  5.00 19   .26 6.821.6 NEV - 2.7
92 JUL 26 2002 31.70 38 50.33 122 45.24  0.83 21   .11  .3  .9 GEY   2.1

92 JUL 26 2100  1.64 38 29.63 118 31.59  9.04 18   .45 3.610.9 MOL   2.7
92 JUL 26 2240 24.75 38 47.60 122 44.16  3.03 26   .14  .3  .7 GEY   2.1
92 JUL 27 1343  8.26 36 18.68 120 52.90  5.97 30   .14  .4  .8 BIT   2.0
92 JUL 27 1705 41.83 37 39.71 118  2.43  1.49 15   .11 3.5 8.8 WHI * 2.2
92 JUL 27 1926 27.94 36 51.87 121 25.04  7.21 93   .21  .3  .4 HOL   2.9
92 JUL 27 2207 28.09 36 21.95 120 44.66 11.88 26   .18  .7  .6 CRV   2.1
92 JUL 27 2316 23.35 36 56.28 121 26.16  5.44 83   .21  .3  .7 HOL   2.5
92 JUL 28  300  5.13 38 47.42 122 46.21  2.02 37   .18  .3  .8 GEY   2.5
92 JUL 28  354 49.22 36 35.26 118 28.29  5.00 13   .1711.3 6.7 KAI - 2.4
92 JUL 28  951 10.78 40 22.77 124 36.42 19.66  7   .14 3.9 1.1 MEN   2.6

92 JUL 28 1011 52.85 38  2.69 118 45.67  5.63 19   .10 1.1 6.3 MOL   2.2
92 JUL 28 1108 14.50 37 38.00 118 55.18  9.39 13   .13  .7  .8 SMO   2.3
92 JUL 28 1747 15.67 36 35.92 121 11.92  2.46 40   .09  .2  .5 PIN   2.3
92 JUL 29  421 24.56 36  8.30 120  1.75  8.53 34   .19  .7  .9 COA   2.3
92 JUL 29  529 50.52 36  7.81 120  2.38  8.09 26   .21  .8  .8 COA   2.1
92 JUL 29 1011 24.60 36  8.12 120  2.41  8.35 17   .21  .8  .9 COA   2.1
92 JUL 29 1101 27.02 35 36.56 118 16.45  9.15  8   .09  .5 1.2 WWF   2.6
92 JUL 29 1128 41.76 37 39.23 118  3.88  1.39 17   .15 4.810.4 WHI * 2.2
92 JUL 29 1457 55.02 37 59.04 118 43.28  5.87 16   .08  .8 2.7 MOL   2.1
92 JUL 29 2054  9.18 37 29.50 118 48.67  7.67 31   .11  .4 1.2 MOR   2.2
92 JUL 29 2205 12.51 40 22.83 124 16.85 10.39 19   .13  .6  .4 MEN   2.7

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
-----------------------------------------------------------------------------
JUL 23
094910.6* 17.413S 179.747W 500G 4.5     0.8  32 FIJI ISLANDS REGION
201243.5  39.822N  24.294E  10G 5.2 5.1 0.9  49 AEGEAN SEA
214811.6* 53.030N 158.995E 109D 5.1     0.8  45 NEAR EAST COAST OF KAMCHATKA
221102.6& 40.177N 124.378W   5                5 NEAR COAST OF NORTHERN CALIF.
        <BRK-P>. ML 3.3 (BRK), 3.2 (GS). Felt at Rio Dell.
JUL 24
020924.2   6.950S 149.720E  44D 5.6 5.5 1.0  62 NEW BRITAIN REGION, P.N.G.
072354.7  34.510N 116.546W   5G         0.7  18 SOUTHERN CALIFORNIA. MD 3.9
                                                (PAS). ML 3.7 (GS).
115134.9? 39.58 N 143.21 E  31D 4.6 4.5 0.9  25 OFF EAST COAST OF HONSHU, JAPAN
142657.9*  7.133S 150.260E  36D 5.4 4.4 1.3  22 NEW BRITAIN REGION, P.N.G.
181434.8  33.940N 116.325W   5G         0.6  28 SOUTHERN CALIFORNIA. MD 4.7
        (PAS). Felt in large parts of southern California, including Los
        Angeles, Orange, Riverside, San Bernardino and San Diego Counties.
JUL 25
025330.7  38.730N 142.968E  33N 5.4 5.4 1.0  75 NEAR EAST COAST OF HONSHU,
                                                JAPAN. Mo=7.9*10**17 Nm (PPT).
043158.9  33.943N 116.351W   5  4.7     1.0  31 SOUTHERN CALIFORNIA. MD 4.7
        (PAS). Felt in many parts of southern California including Los Angeles,
        Orange, Riverside, San Bernardino and San Diego Counties.
050935.9  59.379N 153.625W 125*         0.6  17 SOUTHERN ALASKA
091221.2   0.897N  25.206W  10G 5.4 5.0 0.9  27 CENTRAL MID-ATLANTIC RIDGE
102708.9  34.273N 116.920W   5G         0.7  16 SOUTHERN CALIFORNIA. MD 3.7
                                                (PAS). ML 3.6 (GS).
151113.5  35.915N 116.748W   5G         1.1  18 CENTRAL CALIFORNIA. ML 3.4 (GS).
170219.0  33.969N 116.339W   5G         0.8  16 SOUTHERN CALIFORNIA. MD 3.7
                                                (PAS). ML 3.6 (GS).
JUL 26
105339.8  61.749N 150.229W  33N         0.5  11 SOUTHERN ALASKA
152524.9  50.251N 129.606W  10G 4.5     1.1  43 VANCOUVER ISLAND REGION
JUL 27
041910.8  50.220N 129.944W  10G 4.7     1.1  50 VANCOUVER ISLAND REGION
042130.9  50.233N 130.013W  10G 4.8     0.8  49 VANCOUVER ISLAND REGION
050139.9  50.237N 129.813W  10G 4.2     1.1  30 VANCOUVER ISLAND REGION
123412.6? 52.54 N 158.19 E 135D 4.7     0.8  36 NEAR EAST COAST OF KAMCHATKA
193410.9  51.451N 157.268E 124D 5.3     0.8  74 NEAR EAST COAST OF KAMCHATKA
JUL 29
043050  Q 39.6  N 143.7  E  33N     5.8 0.7  63 OFF EAST COAST OF HONSHU, JAPAN
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