From: andy@pangea.Stanford.EDU (Andy Michael USGS Guest)
Newsgroups: sci.geo.geology,ca.earthquakes
Subject: N. CA, USA, and World Quake Report 12/10-16/92
Date: 18 Dec 1992 08:07:42 GMT
Organization: Stanford Univ. Earth Sciences
Distribution: world
NNTP-Posting-Host: pangea.stanford.edu

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
 December 10 - 16, 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  
    
    During the 7-day period ending at midnight on Wednesday, December 16,
1992 the U.S. Geological Survey office in Menlo Park recorded 35
earthquakes of magnitude one (M1) and greater within the San Francisco Bay
area shown in Figure 1.  Eight were as large as M2.0 including five M3.0
earthquakes on the creeping segment of the San Andreas two miles west of
San Juan Bautista.  This total compares to 22 earthquakes that were
recorded during the previous 7-day period, four of which were as large as
M2. 
    The Bay Area was generally quiet during the past week, with the
exception of the activity on the creeping segment of the San Andreas west
of San Juan Bautista (#1 in Fig. 1).  This is the same area that
experienced a small swarm on December 8th that was capped by one M3.0
event.  This week's swarm began Thursday evening with three M3 events
within a three hour period.  Five M1-2 events followed over the next two
days before another two M3 earthquakes occurred Saturday morning.  The
area remained active throughout the rest of the week, producing another
nine M1 aftershocks.  This swarm is the most activity this section of the
San Andreas has experienced in the past two years.  
    The only other earthquake as large as M2 occurred late Tuesday night
on the Quien Sabe fault about 3 miles northeast of Tres Pinos (#3/1).
        
Northern California

    Activity was down throughout the rest of northern and central
California during the past week.  Outside of the activity near San Juan
Bautista, discussed above, there were no earthquakes as large as M3 within
the area of the northern California Seismic Network.  
    The Cape Mendocino area experienced minimal activity with just three
M2.5 events in the area near Petrolia (#3/2).  Slightly north of the Cape,
a M2.2 occurred Tuesday morning about 17 miles southwest of Eureka (#6/2). 
With a focal depth of 21 km, it is likely that this earthquake occurred
along the interface between the subducting Gorda Plate and the overlying
North American plate.  There was also a M2.1 in the northern Coast Range
about 16 miles north-northeast of Point Arena  Monday night (#5/2). 
    In central California the only earthquake of note was a M2.1 event at
the southern end of the Parkfield segment of the San Andreas (#2/2).  This
small earthquake occurred last Friday, following a small flurry of small
events the previous Tuesday (see last week's summary for details).  
    Seismicity in eastern California was also minimal with a M2.3 near
Bridgeport (1/2), a M2.1 10 miles east of Truckee (#4/2), and a M2.2
beneath the eastern Sierra Nevada, about 34 miles southeast of Yosemite
Valley. 
      
Long Valley Caldera
    
    For the first time since mid-October there were no earthquakes as
large as M2 within the Long Valley caldera.  Activity was limited to five
M1 events, all in the vicinity of the south moat area.  South of the
caldera, M2 earthquakes occurred near Mt. Hopkins (#1/3) and in the Silver
Pass area (#2/3). 

USA Seismicity

   There were several earthquakes of note in the lower 48 states according
to information supplied by the National Earthquake Information Service
(NEIS).  Perhaps the most interesting domestic earthquake of the week was
a M3.6 in central Oklahoma that occurred Wednesday night (#5/4).  It
occurred about 20 miles southwest of Norman, near the town of Lindsay,
where it was reported to have been felt.  The seismicity map of the United
States (Goter, et.al., 1991) shows that this area south of Norman has
experienced numerous earthquakes in the past 20 years, all less than M4. 
It appears to be one of the more active seismic zones in the central U.S.,
second only to the New Madrid zone that extends from the Arkansas-
Tennessee border north into the southern parts of Missouri and Illinois. 
   A M4.3 occurred offshore of northern Oregon on Monday (#4/4).   The
location places it in the central Juan de Fuca plate, just north of the
Blanco Fracture zone.
   Aftershocks continue to dominate the earthquake picture in southern
California.  Both the Barstow and Landers aftershock zones were
represented, the latter with a M3.9 last Thursday evening (#1/4), the
former with a M3.6 on Saturday evening (#3/4).  Finally, a M3.0 occurred
last Friday morning near the northern end of the Imperial fault, south of
the Salton Sea (#2/4).  
            
The Planet Earth

   One of the most lethal earthquakes of recent years occurred this past
week. On December 12 a Ms7.5 (Mb6.6) occurred near the southern coast of
the island of Flores, along the southern rim of the Indonesian archipelago
(#1/5).  Between the earthquake and the tsunami that it generated, nearly 
2500 people were killed or were missing in the Flores region. Over 500
people were injured and at least 40,000 were left homeless.  Approximately
90% of the buildings were destroyed at Maumere and up to 80% of the
structures on the island of Flores were damaged or destroyed.  Tsunami
run-up of 300 meters was reported on Flores with wave heights as great as
25 meters.  Landslides and ground cracks were reported at several
locations around the island.  The earthquake was felt as far away as Ujung
Pandang, Sulawesi, and Timor.   Two M5 aftershocks were recorded in the
same location within a day of the mainshock.
    The earthquake was produced by the subduction of the Indo-Australian
plate beneath the southeastern Eurasian plate.  The most recent comparable
activity in the Flores area was a Mb7.2 event in late August of 1991. 
    Other notable earthquakes around the world, all less than M6, were
primarily concentrated along the western Pacific margin.  They included a
M5.4 in the Rat Islands of the Aleutian chain (#3/5), a M5.2 off the east
coast of Mindanao, Philippine Islands (#6/5),  a M5.7 in the Vanuatu
Islands (#4/5), and a M5.2 south of the Kermadec Islands (#5/5).
     
 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 DEC 10 2113 45.54 38 14.62 119 28.08  7.45 14 2 .19  .914.0 WAK - 2.5
92 DEC 11  512 14.06 36 50.03 121 34.46  8.56102 6 .22  .3  .4 SJB   3.1
92 DEC 11  729 59.22 36 50.90 121 34.56  4.44 86 1 .23  .3  .5 SJB   3.3
92 DEC 11  804 21.59 36 50.96 121 34.63  4.40 87 2 .21  .3  .4 SJB   3.2
92 DEC 11 1317 36.09 37 28.72 118 48.69 10.06 36 1 .09  .3  .8 MOR   2.9

92 DEC 11 2215 33.14 35 48.33 120 21.50  8.37 27   .11  .3  .6 GOL   2.2
92 DEC 12 1118 50.67 36 51.28 121 34.74  4.13 60 2 .18  .3  .4 SJB   2.5
92 DEC 12 1553 46.17 36 51.15 121 35.15  4.97106 1 .22  .2  .3 SJB   3.7
92 DEC 12 1558 52.47 36 51.10 121 34.93  4.53101 1 .22  .2  .4 SJB   3.7
92 DEC 12 1704 55.89 36 49.39 121 33.14  6.98 82 3 .20  .2  .5 SJB   2.7

92 DEC 12 1824 32.00 38 47.89 122 47.01  0.80 25   .14  .3  .7 GEY   2.1
92 DEC 12 1915 24.71 37 28.28 118 54.97 17.91 33   .09  .4  .9 SIL   2.1
92 DEC 13  125 23.91 38 47.07 122 45.38  2.34 20   .09  .3  .7 GEY   2.1
92 DEC 13 1146  9.25 40 22.95 124 20.82  8.61 11 1 .13  .7  .4 MEN   2.1
92 DEC 13 2249 30.25 36 15.51 120 37.06  9.44 34 1 .16  .3  .4 COA   2.2

92 DEC 13 2303 53.15 40 18.92 124 34.89 16.88 12 1 .17 2.5  .7 MEN   2.5
92 DEC 14  413 14.28 39 18.43 119 58.82  8.95 18 2 .16 1.3 3.1 WAK   2.3
92 DEC 14 1745  7.89 40 18.28 124 26.63 12.20 15 1 .10  .8  .4 MEN   2.5
92 DEC 15  535 33.97 39  9.82 123 34.85  0.14 28 2 .11  .3 1.6 PAR   2.1
92 DEC 15 1833 39.06 40 36.01 124 23.85 20.99 13 1 .15 1.6  .6 EUR   2.2

92 DEC 15 2212 44.78 38 47.15 122 46.24  3.22 35 1 .12  .2  .6 GEY   2.5
92 DEC 16  241 19.73 40 18.20 124 26.34 10.40 14 1 .08  .7  .3 MEN   2.5
92 DEC 16  626 45.68 36 50.40 121 18.04  4.41 58 3 .10  .2  .4 QUI   2.3
92 DEC 16 1630 16.82 37 15.98 119 24.04  5.99 12   .11 1.311.8 KAI - 2.2
92 DEC 16 1938 23.02 36 34.08 121  4.25  6.58 47   .19  .3  .7 BVL   2.1

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
------------------------------------------------------------------------------
DEC 10
135443.8* 24.124S 178.549E 600G 4.6     0.9  22 SOUTH OF FIJI ISLANDS
180335.0   6.067N  82.517W  10G 4.8 4.4 1.0  43 SOUTH OF PANAMA
182333.2  34.161N 116.417W   5G         0.7   8 SOUTHERN CALIFORNIA. MD 3.3

DEC 11
013832.4  34.258N 116.367W   5G         0.8  25 SOUTHERN CALIFORNIA. MD 3.9
051212.4  36.741N 121.716W  10G         0.6  15 CENTRAL CALIFORNIA. ML 3.1
072958.1  36.766N 121.639W  10G         0.8  17 CENTRAL CALIFORNIA. ML 3.2
124725.4* 33.086N 115.642W   5G         1.2   7 SOUTHERN CALIFORNIA. MD 3.0
131736.3  37.493N 118.803W   5G         0.6  11 CALIFORNIA-NEVADA BORDER REGION.
                                                ML 3.2 (BRK)1
193427.0* 41.814N  20.645E  33N         0.7  28 ALBANIA. ML 4.2 (ROM).

DEC 12
003143.4  34.323N 116.828W   5G         0.9  11 SOUTHERN CALIFORNIA. MD 3.4
050207.2  34.554N 141.644E  33N 5.0     1.1  57 OFF EAST COAST OF HONSHU, JAPAN
052927.2?  8.43 S 122.30 E  33N 6.6 7.5 1.2  20 FLORES REGION, INDONESIA.
        Mo=8.0*10**20 Nm (PPT). At least 2,484 people killed or missing in the
        Flores region, including nearly 1,500 at Maumere and 750 on Babi. More
        than 500 people were injured and 40,000 left homeless. 19 people were
        killed and 130 houses destroyed on Kalaotoa. Severe damage, with
        approximately 90 percent of the buildings destroyed at Maumere by the
        earthquake and tsunami; 50 to 80 percent of the structures on Flores
        were damaged or destroyed. Damage also occurred on Sumba and Alor.
        Tsunami run-up of 300 meters with wave heights of 25 meters was reported
        on Flores along with landslides and ground cracks at several locations
        around the island. Felt as far away as Ujung Pandang, Sulawesi and
        Kupang, Timor. 
063831.4   8.501S 122.005E  33N 5.6     1.0  36 FLORES REGION, INDONESIA
142056.7  25.553N  91.274E  33N 5.0     0.6  21 INDIA-BANGLADESH BORDER REGION
155344.9  36.748N 121.754W  10G         0.8  22 CENTRAL CALIFORNIA. ML 3.7 (GS).
        Felt in the San Juan Bautista area.
155851.1  36.744N 121.713W  10G         0.8  14 CENTRAL CALIFORNIA. ML 3.6 (GS).
        Felt in the San Juan Bautista area.
214310.4   8.670S 122.033E  33N 5.5 4.7 1.0  35 FLORES REGION, INDONESIA

DEC 13
013921.5* 37.938N 142.944E  19* 3.9     1.1  20 OFF EAST COAST OF HONSHU, JAPAN
041402.7  34.984N 117.007W   5G         0.5  18 SOUTHERN CALIFORNIA. MD 3.6
122956.2* 51.626N 179.812E  75D 4.8     1.1  43 RAT ISLANDS, ALEUTIAN ISLANDS

DEC 14
025207.4  52.062N 178.641E 131D 5.4     1.2 105 RAT ISLANDS, ALEUTIAN ISLANDS.
                                                Felt strongly on Amchitka.
041512.2* 19.501N 109.226W  10G 4.7     0.9  36 REVILLA GIGEDO ISLANDS REGION
073951.7? 15.90 S 168.94 E  72D 5.7     0.6  62 VANUATU ISLANDS
191303.4* 33.542S 179.443E 223D 5.2     0.9  30 SOUTH OF KERMADEC ISLANDS

DEC 15
124607.5*  8.688N 126.732E  33N 5.2 4.9 1.1  18 MINDANAO, PHILIPPINE ISLANDS
145926.5* 44.977N 128.835W  10G 4.3     0.8  13 OFF COAST OF OREGON

DEC 17
071803  Q 34.9  N  97.5  W  10G         1.2  10 OKLAHOMA. mbLg 3.6 (GS).