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 16 - 23, 1992
                                     
                         Data and text prepared by
             Steve Walter, Nan Macgregor-Scott, 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 22, 1992
the U.S. Geological Survey office in Menlo Park recorded 14 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 17 earthquakes recorded during the previous 7-day period, none of
which were as large as M2.0. 
   Most activity occurred early in the week, primarily in the southern
part of the Bay Area on both the San Andreas and Calaveras faults.  Last
Thursday morning a M2.4 occurred on the southern Calaveras, about 1 mile
southwest of Hollister (#1/1).  That same afternoon another M2.4 occurred
on the San Andreas about 5 miles east of Watsonville (#2/1).  On Saturday
evening small M2 earthquakes occurred on both the central Calaveras, about
12 miles north of Morgan Hill (#3/1), and on the San Andreas, about 3
miles west of San Juan Bautista (#4/1).  
   Also on Saturday evening there was a M2.1 in the East Bay, about 12
miles north of Livermore (#5/1).  This is the same location as a M3.4
event that occurred in July of last year and about two miles east of the
M5.9 Livermore earthquake that occurred on January 24, 1980.

Northern California
    
     The week began with a M4.0 earthquake about 12 miles north-northeast
of Red Bluff last Thursday morning (#1/2).  This event, which was felt
from Redding to Sacramento, is the largest earthquake seen in this area in
the 11 years that the USGS has maintained a seismic network in this part
of the state.  The focal depth of the earthquake was nearly 25 km, deep
when compared to earthquakes in most other areas of the state, but not
atypical of earthquakes in a zone that extends from Lake Shasta south to
just west of Sutter Buttes.  Earthquakes in this zone generally are deeper
than normal, ranging from 10 to 30 km.  
   Several other unusually deep earthquakes were recorded in the state in
the two days following the Red Bluff earthquake.  Just eighteen hours
later a M2.5 event occurred  11 miles north of Redding (#2/2).  Like the
Red Bluff event, it occurred at a depth of 25 km.  Ten hours later a 30km-
deep, M2.8 event occurred beneath the central Sierra Nevada, about 38
miles northeast of Fresno (#4/2).  This is nearly the same location,
though slightly deeper, as a M2.2 event that occurred here in late
January.  The week's final deep earthquake occurred four hours later, a
M2.8 event that was located 26 km beneath the San Joaquin Valley, about 33
miles southeast of Avenal (#5/2).  
    Several areas continued to experience earthquake activity over three
weeks after the activity was triggered by the M7.4 Landers earthquake in
southern California.  These areas include the Mono Lake basin (#7/2), the
White Mountains area southeast of Mono Lake, and the Burney area north of
Lassen Peak (#3/2).  
    One area that began to experience seismicity only in the past week was
the Carson Lake area, 20 miles east of Carson City, NV (#8/2).  Several
earthquakes larger than M3 shook the area on Monday, including a M4.1
event on Monday afternoon that was felt in the Fallon and Silver Springs
areas.
    Aftershocks in the Cape Mendocino area continued to decay nearly three
months after a M7.0 shook the area.  During the past week only six
aftershocks larger than M2 were recorded in the area (#9/2), the largest a
M2.6 that occurred last Thursday night about 4 miles southwest of Eureka
    Just after midnight last Friday a M2.9 earthquake occurred about 20
miles east of Mount Shasta City (#6/2).  It occurred at a shallow depth
beneath the north side of Black Fox Mountain.  This is the first
earthquake to occur in this particular area since the USGS began
monitoring seismicity in the region in 1981 and the largest earthquake in
the Mount Shasta/Medicine Lake area in at least the past 18 months.
    Activity along the San Andreas system remained subdued.  Only two M2
earthquakes were recorded south of the Bay Area, both on the creeping
segment of the fault.  North of the Bay Area, a M2.3 event occurred last
Thursday along the Maacama fault west of Clear Lake. Just after noon on
Wednesday a M2.2 event occurred on the Rogers Creek fault, about 2 miles
northeast of Santa Rosa (#10/2).

Long Valley Caldera
        
    Activity within the caldera continued to decline from the high levels
that immediately followed the Landers earthquake.  During the past week
only five earthquakes occurred in the caldera, none as large as M2.  All
five were located in the south moat area, the main locus of activity since
the caldera began to experience significant activity in 1980.  
   A small cluster of earthquakes occurred in the Sierra Nevada terrane
south of the caldera last Friday evening (#2/3).  The largest of these,
M3.8 event, was felt in Mammoth Lakes, just 11 miles to the north.
   The only other M2 earthquake in the area was a M2.1 event that occurred
Monday evening in the Mount Morrison area (#3/3).  

USA Seismicity
    
   Aftershocks to the June 28 Landers earthquake continued to be felt in
southern California during the week, though the rate of activity continues
to decline.  Only three aftershocks as large as M4 were recorded during
the week, the largest a M4.5 event that occurred after noon Monday (#3/4).
   A number of earthquakes were recorded outside of California during the
past week by the National Earthquake Information Center in Golden, CO. 
Most occurred in Nevada including a pair of M3.1 events in southeast Nye
county east of Tonopah (#1/4), a cluster of M3-4 events near Carson Lake
(#5/4-discussed above), and a M4.0 event northeast of Eureka (#6/4). 
Increased activity was also reported in the Yellowstone area of Wyoming. 
A M3.7 event just after midnight on Monday was felt in parts of
Yellowstone National Park (#4/4).
The Planet Earth

   A large earthquake occurred July 18 off the east coast of Honshu, Japan
(#4/5).  This Ms6.9 event was felt from Tokyo to the northeast coast of
Hokkaido and produced a tsunami with wave heights of up to 46 cm along
east coast of Honshu.  The mainshock was preceded by M4.7 and M5.2
foreshocks and was followed by numerous aftershocks, including ten that
were as large as M5.  
   Several other earthquakes occurred along the margin of the northwest
Pacific including a Mb5.9 event east of the Kuril Islands (#1/5) and a
Mb5.0 event in eastern Siberia (#2/5).  In the southwestern Pacific, a
pair of M5 events occurred near the eastern coast of Papua New Guinea and
a Ms5.6 earthquake occurred in the Tonga Islands region (#5/5).
   In the western hemisphere, a Mb5.7 earthquake occurred near the central
coast of Peru (#3/5) and a Mb4.8 occurred in central Colombia.  
   Finally, a Ms6.7 earthquake occurred north of the Arctic circle, along
a mid-oceanic spreading ridge beneath the Greenland sea (#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 16 1208 10.64 38 42.70 119 40.35  5.38 11   .09 7.2 3.6 WAK - 2.6
92 JUL 16 1341 51.78 36 50.04 121 24.62  9.22 76   .17  .3  .4 HOL   2.4
92 JUL 16 1342 59.59 39  9.57 123  9.63  5.31 16   .08  .4 1.3 MAA   2.3
92 JUL 16 1537 59.73 40 20.29 122 11.42 24.55 27   .27  .6 1.1 SHA   4.0
92 JUL 16 1714 35.06 38 47.82 122 48.47  3.76 26   .15  .3  .7 GEY   2.6
92 JUL 16 2106 50.33 36 16.47 120 50.35  7.04 32   .27  .6 1.2 BIT   2.0
92 JUL 16 2319 24.69 36 54.34 121 39.58 10.08 80   .18  .3  .5 SJB   2.4
92 JUL 16 2338 40.22 38  0.61 118 41.61  4.27 13   .23 2.8 5.8 MOL   2.0
92 JUL 17  250 46.88 40 14.32 124 20.58  3.96  8   .14 1.4  .6 MEN   2.5
92 JUL 17  505 47.53 40 44.60 124 12.89  9.53 16   .16  .7  .9 EUR   2.6

92 JUL 17  952 22.04 40 42.78 122 29.05 25.22 10   .26 1.2 2.3 SHA   2.5
92 JUL 17 1125 20.40 40 21.44 124 14.81 10.18  8   .06  .3  .9 MEN   2.1
92 JUL 17 1305 49.08 40 54.12 121 34.02  0.80 15   .18  .7 4.2 SHA * 2.3
92 JUL 17 1939  7.51 37  9.03 119 19.49 29.67 31   .10  .9 1.6 KAI   2.8
92 JUL 17 2337 57.56 35 41.46 119 40.66 26.29 33   .21 1.1 1.9 BAK   2.8
92 JUL 18  454 42.70 37 29.51 118 57.15  3.84 33   .09  .3 1.4 SIL   3.1
92 JUL 18  658 39.66 37 29.56 118 57.04  3.94 31   .12  .3 1.5 SIL   3.8
92 JUL 18  708  7.64 41 23.54 121 53.86  2.20 10   .15  .5 1.2 MOD   2.9
92 JUL 18  951 10.40 37 26.74 118 21.29  6.76 20   .10  .4  .9 CHV   2.2
92 JUL 18 2057 50.21 38 47.71 122 46.56  4.60 33   .17  .3  .6 GEY   2.1

92 JUL 19   51 24.04 40 24.12 124 42.83 11.55  7   .10 4.8 2.2 MEN   2.1
92 JUL 19  159 10.47 37 17.83 121 40.51  2.55 42   .09  .2  .6 SFL   2.1
92 JUL 19  316 59.91 36 51.11 121 35.24  6.78 50   .19  .3  .5 SJB   2.0
92 JUL 19  657 24.10 37 50.70 121 45.84 14.66 34   .15  .5  .6 GRN   2.1
92 JUL 19  822 56.31 36 36.34 121 12.78  8.91 49   .12  .2  .4 PIN   2.2
92 JUL 19  855  1.71 37 29.67 118 56.98  0.42 19   .10  .6 8.9 SIL - 2.0
92 JUL 19 1124 58.57 38 48.75 122 50.12  0.02 17   .12  .3 1.7 GEY * 2.0
92 JUL 19 1512 55.61 37 56.11 118 34.84  7.04 24   .14 1.6 3.5 MOL   2.2
92 JUL 20  108 12.47 37 38.46 118  6.73  0.10 16   .11 3.5 4.8 WHI * 2.1
92 JUL 20  109 21.48 37 39.55 118  2.74  1.36 20   .16 3.311.8 WHI - 2.3

92 JUL 20 1519  5.61 39  9.58 119 25.46  5.01  9   .1410.0 9.1 WAK - 2.4
92 JUL 20 1722 26.38 39 13.06 119 29.55  3.98 13   .2611.2 8.1 WAK * 3.1
92 JUL 20 1736  8.11 39 17.22 119 18.42  5.04 39   .33 2.524.2 NEV - 3.4
92 JUL 20 1906 58.53 39 17.40 119 18.76  0.16 38   .37 2.3 8.0 NEV * 3.7
92 JUL 20 1915 53.06 39 12.60 119 29.39  3.14 13   .2310.6 9.9 WAK * 3.0
92 JUL 20 2009 33.63 39 15.83 119 21.23  1.16 45   .24 1.2 5.4 WAK   4.1
92 JUL 21  150  7.72 39 13.82 119 33.00  2.53 14   .3711.411.8 WAK * 3.1
92 JUL 21  446 23.32 37 32.91 118 51.67 10.99 34   .13  .4 1.0 MOR   2.1
92 JUL 21 1158 24.71 39 13.23 119 23.45  1.25 16   .19 2.1 7.4 WAK * 3.1
92 JUL 21 1301 48.60 39 11.77 119 29.02  3.85 16   .20 9.9 7.3 WAK * 2.9

92 JUL 21 1344  6.70 38 48.52 122 46.47  1.50 23   .16  .3 1.3 GEY   2.1
92 JUL 22   54  1.19 40 20.49 124 29.79 15.02  8   .20 3.2 1.1 MEN   2.5
92 JUL 22 1013  5.21 38  3.29 118 51.51  6.38 26   .13 1.913.0 MOL - 2.4
92 JUL 22 1935  4.30 38 27.72 122 41.08  7.75 34   .17  .3  .9 ROG   2.2
92 JUL 23  629  3.73 40 17.84 124 22.93  8.58  9   .06 1.1  .7 MEN   2.3

                                    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 16
151129.9& 61.670N 150.910W  53               63 SOUTHERN ALASKA. <AEIC>. ML 2.8
153800.0& 40.337N 122.197W  17               14 NORTHERN CALIFORNIA. <BRK-P>. MD
        4.0 (GM). ML 3.9 (BRK). Felt in the Redding-Chico-Sacramento area.
183303.1  38.323N 116.159W   5G         0.7  12 NEVADA. ML 3.1 (GS).
215820.0  34.925N 116.915W   5G         0.5  15 SOUTHERN CALIFORNIA. MD 3.5
JUL 17
041136.2  44.381N 150.392E  33N 5.9 5.1 0.9  50 EAST OF KURIL ISLANDS
060012.5  38.387N 116.120W   5G         0.8  11 NEVADA. ML 3.1 (GS).
110301.7* 60.807N 166.997E  33N 5.0 4.8 1.0  60 EASTERN SIBERIA, RUSSIA
184558.9* 10.470S  78.298W  46D 5.7 5.1 0.7  64 NEAR COAST OF PERU.
        Mo=1.6*10**18 Nm (PPT). Felt at Barranca, Chimbote, Huacho and Huaraz.
        Felt (III) at Lima.
JUL 18
014053.7?  4.44 N  75.28 W 150G 4.8     0.8  35 COLOMBIA. Felt in Antioquia,
                                                Caldas, Quindio and Risaralda
                                                Departments.
075746.5*  6.446S 147.900E  33N 5.1 5.1 1.1  13 EASTERN NEW GUINEA REG., P.N.G.
081517.2  39.511N 143.167E  33N 4.7     1.0  35 OFF EAST COAST OF HONSHU, JAPAN
082001.8  39.432N 143.234E  33N 5.2     0.9  66 OFF EAST COAST OF HONSHU, JAPAN
083659.2  39.408N 143.353E  33N 5.9 6.9 0.9 118 OFF EAST COAST OF HONSHU, JAPAN.
        Mo=2.5*10**19 Nm (PPT). Felt (III JMA) at Aomori, Hachinohe, Ishinomaki,
        Miyako, Sakata and Sendai; (II JMA) at Akita and Fukushima; (I JMA) at
        Kofu, Tokyo, Tateyama and Utsunomiya, Honshu. Also felt (II JMA) at
        Kushiro, Nemuro and Obihiro, Hokkaido. Tsunami generated with maximum
        wave heights (peak-to-trough) of 46 cm. at Ofunato, 42 cm. at Miyako, 28
        cm. at Aikawa and 24 cm. at Hachinohe. 
083906.0* 39.724N 143.019E  33N 5.8     1.1  45 OFF EAST COAST OF HONSHU, JAPAN
094505.1? 39.77 N 143.00 E  33N 4.6     0.8  16 OFF EAST COAST OF HONSHU, JAPAN
102013.1  39.526N 143.011E  33N 5.8 6.1 1.0  96 OFF EAST COAST OF HONSHU, JAPAN.
105940.3  39.404N 143.206E  33N 5.1     1.0  75 OFF EAST COAST OF HONSHU, JAPAN
110652.0? 39.33 N 143.37 E  33N 4.6     0.7  13 OFF EAST COAST OF HONSHU, JAPAN
111013.2? 39.50 N 143.49 E  33N 4.8     0.8  25 OFF EAST COAST OF HONSHU, JAPAN
111113.0? 39.81 N 143.28 E  33N 5.0     1.2  22 OFF EAST COAST OF HONSHU, JAPAN
114614.2* 39.353N 143.467E  33N 4.6     0.5  14 OFF EAST COAST OF HONSHU, JAPAN
114818.4  39.248N 143.164E  13D 5.3     0.8  63 OFF EAST COAST OF HONSHU, JAPAN
120241.7  39.148N 143.174E  33N 5.2     0.8  67 OFF EAST COAST OF HONSHU, JAPAN
135655.2  39.455N 142.996E  33N 5.4 5.3 0.8  66 NEAR EAST COAST OF HONSHU,
144546.7  39.344N 143.261E  33N 4.7     0.8  44 OFF EAST COAST OF HONSHU, JAPAN
153143.2* 22.600S 175.136W  33N 5.1 5.6 0.9  40 TONGA ISLANDS REGION
172712.1  39.716N 143.117E  33N 4.8 5.4 0.8  46 OFF EAST COAST OF HONSHU, JAPAN
181213.3  39.111N 143.156E  33N 5.1 4.9 0.8  55 OFF EAST COAST OF HONSHU, JAPAN
205513.2* 39.545N 143.258E  33N 5.2 5.2 1.0  57 OFF EAST COAST OF HONSHU, JAPAN
211856.7  39.277N 142.959E  33N 5.2 5.6 1.3  77 NEAR EAST COAST OF HONSHU,
213624.8* 30.795N 137.306E 475D 4.9     0.8  51 SOUTH OF HONSHU, JAPAN
JUL 19
003239.5  37.179N 117.241W   5G         0.7  15 CALIFORNIA-NEVADA BORDER REGION.
                                                ML 3.2 (GS).
024008.6*  6.558S 147.680E  33N 4.9     1.2  22 EASTERN NEW GUINEA REG., P.N.G.
JUL 20
044800.2  34.935N 116.938W   5G 4.3     0.9  28 SOUTHERN CALIFORNIA. MD 4.4
070329.1* 44.802N 110.367W   5G         0.9  10 YELLOWSTONE REGION, WYOMING. ML
                                                3.7 (GS). Felt in parts of
                                                Yellowstone National Park.
074649.0* 78.776N   3.938E  10G 5.5 6.7 1.2  44 GREENLAND SEA
131319.0  34.986N 117.006W   5G 4.4     0.9  26 SOUTHERN CALIFORNIA. MD 4.5
190657.1  39.400N 119.087W   5G         1.2  17 NEVADA. ML 3.8 (GS). Felt at
                                                Fernley and Silver Springs.
200931.2  39.335N 119.107W   5G 4.1     0.8  21 NEVADA. Felt in the Fallon
                                                Fernley-Silver Springs area
JUL 21
205805  Q 39.4  N 115.6  W   5G         0.8  22 NEVADA. ML 4.0 (GS).
232209  Q 34.1  N 116.6  W   5G         0.6  18 SOUTHERN CALIFORNIA. ML 4.0

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.