From: andy@pangea.Stanford.EDU (Andy Michael USGS Guest)
Subject: N. CA, USA, and World Quake Report 10/1-7/92
Organization: Stanford Univ. Earth Sciences
Date: Fri, 9 Oct 1992 06:22:32 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
   October 1 - 7, 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, October 7, 1992
the U.S. Geological Survey office in Menlo Park recorded 28 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 week's total
compares to the 17 earthquakes recorded during the previous 7-day period,
only one of which was as large as M2. 
    The largest earthquake during the week was a M2.4 early Tuesday
morning (#4 in Fig. 1).  It occurred about 10 miles northeast of Santa
Cruz where it was reported to have been felt.  With a focal depth of about
13 km, this earthquake occurred on or near the deeper part of the Loma
Prieta rupture zone.   A M2.3 occurred in almost exactly the same location
in early August.  
    Several hours prior to the "Santa Cruz" event, a M2.3 occurred near
the creeping segment of the San Andreas, about 3 miles west of San Juan
Bautista (#3/1).  This is the same area that produced a small cluster of
earthquakes just three weeks ago, the largest of which was a M3.2.
    The only other M2 event occurred last Saturday evening midway between
the Concord and Alamo faults, about 3 miles west of Pittsburg (#2/1). 
This M2.1 event was followed by a M1.7 aftershock.  Both earthquakes
occurred at a depth of about 17 km, somewhat deeper than is typical for
other earthquakes in the Bay Area.
      
Northern California
    
    The most interesting aspect of seismicity in northern and central
California was the number of unusually deep earthquakes that occurred  
beneath the central Sierra Nevada during the week.  Three areas around
Yosemite Valley experienced earthquakes deeper than 30 km.  The first of
these was a cluster of three M2 events that occurred last Thursday night
about 24 miles southeast of Yosemite Valley (#1/2).  All had focal depths
of 32-33 km.  Friday afternoon a M2.2 earthquake occurred 28 miles
southwest of Yosemite Valley; it also had a focal depth of 33 km (#4/2).  
The fifth deep event in this region occurred Monday evening about 31 miles
northwest of Yosemite Valley (#9/2).  It occurred at a depth of 35 km.  
    Over the past 18 years this area of the central Sierra Nevada has
experienced approximately 40 earthquakes that were deeper than 30 km. 
Only once during this period did a comparable number of deep events occur
in such a short time.  Over a 4-week period in late 1985, nine earthquakes
occurred about 20 miles west-northwest of Yosemite, all between 30 and 35
km deep.  Magnitudes ranged from M2.4-M3.3.   
     The Parkfield segment of the San Andreas was also unusually active
during the past week, producing one M3.1 and two M2.7 events (#8/2).  This
is the highest level of activity on this segment in at least the past two
years.  All three earthquakes occurred near Middle Mountain, the area
where the predicted Parkfield earthquake is expected to initiate.  The
Parkfield earthquake prediction, the first officially recognized
scientific prediction of an earthquake in the United States, was issued
in 1985 and predicted that an earthquake of approximately M6 would occur
here before 1993.  
     Cape Mendocino continued to be the most active area in northern
California, producing a small cluster of M2's on Saturday that were
located along the Mendocino fault zone 5 - 7 miles west of Petrolia
(#5/2).  This was followed on Monday by a larger cluster 12 miles west of
Petrolia that included three M3 events.  To the northeast of Cape
Mendocino, about 37 miles east of Eureka, a subduction earthquake occurred
early last Friday morning (#3/2).  Interestingly, it occurred about the
same time the deep events were occurring in the Yosemite Valley area and
had the same focal depth of about 33 km.
        
Long Valley Caldera
        
     For the second straight week activity inside the caldera was
practically nil while felt events occurred in the Sierra Nevada terrane to
the south.   Only three events greater than M1.5 occurred within the
caldera, all in the south moat area.  South of the caldera, the area west
of Mt. Morrison continued to be active, producing two M2.0 events (#1/3). 
The previous week, two M3 events occurred in the same area.   An even more
active cluster occurred early Monday morning 15 miles south-southeast of
Mammoth Lakes, near Grinnell Lake (#2/3).  It started with a M4.1 and was
followed by four M2 aftershocks over the course of the next 80 minutes. 
       
USA Seismicity

    According to the National Earthquake Information Service, the only
notable earthquake in the lower 48 states, outside of California, was a
M3.4 event in south-central New Hampshire just before noon on Tuesday
(#2/4).  The temblor was felt at both Franklin and Laconia, New Hampshire. 
    Aside from two northern California events discussed above, the NEIS
recorded a number of earthquakes in southern California, most aftershocks
to the M7.5 Landers quake of late June.  The largest of these was a M4.3
that occurred just after midnight last Thursday (#1/4).     
            
The Planet Earth

    Seismicity worldwide was relatively low-level during the past week
with no earthquakes as large as M6 recorded anywhere.  The largest
earthquake of the week was a M5.8 in the New Britain region of Papua New
Guinea (#6/5).   Nearly as large was a M5.6 that occurred just off the
coast of central Chile (#1/5).  
     Magnitude 4 earthquakes are generally too small to make the listing
but given the low level of activity last week, I'll take the opportunity
to point out several small felt earthquakes that occurred around the
world.  A M4.5 occurred in central Alaska that was felt at Two Rivers,
Delta Junction, and Fairbanks (#2/5).   Last Friday night a M4.2 occurred
on the big island of Hawaii that was felt at Hilo and throughout the
southeastern part of the island (#3/5).  Later that same night a M4.7
occurred beneath the central Gulf of California that was felt from
Hermosillo to Guaymas in the state of Sonora (#4/5).  Finally a M4.7
occurred late Sunday night beneath the mid-Atlantic Ridge (#5/5).  It was
felt by no one but the strange bottom dwellers that live around the "black
smokers" of the this deep ocean rift.   
 

             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 OCT  1  955 46.99 40 18.19 124 24.45  7.88 18 1 .14  .8  .4 MEN   2.0
92 OCT  1 1957 31.81 35 59.97 119 58.09 11.67 35 1 .24 1.1 1.3 COA   2.2
92 OCT  1 2340 20.97 38 20.68 118 47.35 18.77 14 2 .13  .8 2.0 MOL-  2.5
92 OCT  2    3 58.50 37 34.34 118 51.91  7.74 30   .11  .3  .6 MOR   2.3
92 OCT  2  142 23.90 38 21.74 118 44.78  5.00 13   .09 3.510.6 MOL-- 2.5

92 OCT  2  257 20.34 37 25.64 119 23.04 32.73 17 1 .14  .7 1.8 KAI * 2.3
92 OCT  2  448 12.96 38 21.15 118 46.50 11.25 31 2 .15 1.2 4.8 MOL-  2.2
92 OCT  2  458 30.77 37 25.56 119 22.83 32.06 40 4 .13  .4  .8 KAI-  2.5
92 OCT  2  618 39.61 37 53.43 118 30.08  5.68 26   .10 1.1 1.9 CHV   2.6
92 OCT  2  631 31.46 37 53.53 118 30.07  0.37 17   .10 1.5 7.4 CHV * 2.1

92 OCT  2  945  5.22 37 25.60 119 22.85 31.52 39 3 .14  .4  .8 KAI-  2.4
92 OCT  2 1252 32.46 40 41.57 123 28.87 33.73 15   .13  .6 1.3 EUR   2.2
92 OCT  2 1621  7.35 37 23.60 119 53.47 33.25  8 2 .19 1.8 2.9 KAI   2.5
92 OCT  3  910 23.13 40 18.57 124 24.90  7.72 21   .18 1.2  .5 MEN   2.9
92 OCT  3  911 23.26 40 18.84 124 23.74  7.53 25 2 .15  .6  .3 MEN   2.9

92 OCT  3 1045 46.80 40 18.47 125 19.47 19.02 16 1 .3912.620.8 MEN - 2.5
92 OCT  3 1853 35.22 40 19.24 124 23.06  6.15 20 2 .13  .6  .4 MEN   2.2
92 OCT  3 2110 29.65 40 21.03 125  4.77  8.06 17   .2210.1 8.1 MEN-  2.6
92 OCT  4  346 39.76 38  0.85 121 54.05 17.12 52 2 .20  .4  .6 GRN   2.1
92 OCT  4 1306 25.75 35 58.61 118 21.55  5.44 12   .07  .3 1.2 WWF   3.0

92 OCT  4 1609 35.39 38 26.65 122 38.48  6.44 32 2 .17  .3  .8 ROG   2.3
92 OCT  4 1615 57.75 38 42.18 122 47.26  7.07 26 2 .11  .3  .6 NAP   2.2
92 OCT  4 1816 57.34 35 55.55 120 28.35 10.06 78 6 .12  .2  .2 MID   3.1
92 OCT  5 1140 28.47 37 27.19 118 50.46  8.04 36   .09  .3 1.0 MOR   3.9
92 OCT  5 1225 48.55 37 27.09 118 50.69  8.32 32   .09  .3 1.0 MOR   2.5

92 OCT  5 1240 52.45 37 27.05 118 50.38  0.56 26   .37 1.019.7 MOR   2.5
92 OCT  5 1241 52.53 37 27.12 118 50.60  8.33 35   .09  .3 1.0 MOR   2.6
92 OCT  5 1259 18.46 37 27.18 118 50.85 11.16 22   .09  .4 1.8 MOR   2.0
92 OCT  5 1730 19.09 40 18.94 124 30.95  9.06 20 1 .13 1.0  .4 MEN   2.8
92 OCT  5 1859 32.20 35 55.64 120 28.42  9.87 67 5 .11  .2  .3 MID   2.7

92 OCT  5 2034 55.12 40 18.64 124 31.28  8.27 22 2 .16 1.0  .5 MEN   3.4
92 OCT  5 2141 26.74 40 18.81 124 31.87  8.43 21 1 .16 1.2  .4 MEN   3.0
92 OCT  5 2239 36.05 37 55.63 118 38.04  0.48 23   .09  .7 8.7 MOL - 2.7
92 OCT  6  100 36.26 38  1.09 120  1.79 34.70 17 3 .18 1.0  .5 YOS   2.4
92 OCT  6  107 20.14 40 18.81 124 30.79  8.67 22 1 .15 1.1  .4 MEN   2.9

92 OCT  6  312 14.23 40 24.67 124 33.44 15.70 17 1 .14 1.5  .5 MEN   2.3
92 OCT  6  450 55.01 40 18.74 124 31.40  9.64 13   .15 1.5  .5 MEN   3.5
92 OCT  6  710 39.69 36 50.72 121 34.93  5.44 58   .21  .3  .6 SJB   2.3
92 OCT  6 1138  4.01 37  4.81 121 54.58 13.15 76   .11  .2  .3 LOM   2.4
92 OCT  6 1205 18.39 38 46.98 122 45.19  2.26 35   .13  .2  .6 GEY   2.5

92 OCT  6 2059 17.17 37 27.21 118 50.53  8.32 34 1 .09  .3  .9 MOR   2.2
92 OCT  7   35 24.23 40 21.59 124 16.05 10.78 24 2 .16  .4  .3 MEN   2.8
92 OCT  7  157 22.30 38 48.57 120  9.13  3.15  8   .1411.4 8.7 WAK - 2.0
92 OCT  7 1232 12.10 37 34.15 118 51.51 10.09 18   .09  .4  .8 MOR   2.0
92 OCT  7 1304 28.32 35 58.30 120 31.60  5.62 53 3 .13  .2  .3 MID   2.8

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
-------------------------------------------------------------------------------
OCT 01
081851.9* 39.060S  74.850W  29D 5.6 4.9 0.9  52 OFF COAST OF CENTRAL CHILE.
082634.2* 51.061N 178.284W  33N 4.3     1.3  24 ANDREANOF ISLANDS, ALEUTIAN IS.
115616.3? 11.28 N  86.82 W  33N 4.6     1.4  21 NEAR COAST OF NICARAGUA
133253.8  63.798N 148.432W 113  3.6     0.8  94 CENTRAL ALASKA. Felt at
        Cantwell, Eielson AFB, Fairbanks, Fox and Healy.
133837.0  64.127N 146.094W  33N 4.5     1.1  21 CENTRAL ALASKA. ML 4.5 (AEIC),
        4.4 (PMR). Felt (V) at Two Rivers, (IV) at Delta Junction and (II) at
        Fairbanks.
134750.5? 40.35 N 125.52 W  10G         1.2   7 OFF COAST OF NORTHERN CALIFORNIA
163705.5  51.069N 178.103W  47D 4.7     1.1  55 ANDREANOF ISLANDS, ALEUTIAN IS.
                                                Felt on Adak.
205230.2  63.309N 151.243W   8          1.0  65 CENTRAL ALASKA. ML 3.4 (PMR).
220858.9* 10.653N  86.867W  33N 4.5     1.2  19 OFF COAST OF COSTA RICA. MD 4.6
OCT 02
063033.5? 26.46 S 113.78 W  10G 5.0 4.6 0.9  21 EASTER ISLAND REGION
070505.9  51.084N 177.825W  43D 4.6     1.0  54 ANDREANOF ISLANDS, ALEUTIAN IS.
071956.3  34.549N 116.653W   5G         1.2  39 SOUTHERN CALIFORNIA. MD 4.3
105046.5* 30.757S 177.557W  33N 5.2 5.4 1.0  23 KERMADEC ISLANDS, NEW ZEALAND
121212.8  34.575N 116.612W   5G         0.8  16 SOUTHERN CALIFORNIA. MD 3.5
154954.2  33.977N 116.316W   5G         0.7  10 SOUTHERN CALIFORNIA. MD 3.0
172842.6* 50.922N 177.916W  33N 4.4     1.3  22 ANDREANOF ISLANDS, ALEUTIAN IS.
192956.3?  0.10 N 122.81 E 134* 5.4     0.8  19 MINAHASSA PENINSULA, SULAWESI
214217.0  34.020N 117.184W   5G         0.8  16 SOUTHERN CALIFORNIA. ML 3.0
        (GS). Felt at San Bernardino and Redlands.
OCT 03
055141.8& 19.350N 155.070W   7  4.2           9 HAWAII. <HVO-P>. MD 4.3 (HVO).
        Felt at Hilo, in the Kona District,& the southeastern Island of Hawaii.
072951.5  34.490N 116.422W   5G         1.1   9 SOUTHERN CALIFORNIA. MD 3.0
073726.5* 27.445N 111.401W  22? 4.7 5.3 1.3  52 GULF OF CALIFORNIA. Felt at
        Bahia Kino, Guaymas and Hermosillo, Sonora.
074225.8  51.177N 178.336E  33N 5.1 4.9 0.8  43 RAT ISLANDS, ALEUTIAN ISLANDS
091908.6* 56.492N 152.732W  33N 4.9     1.2  22 KODIAK ISLAND REGION
135637.6? 22.78 N 120.94 E  33N 4.8     1.1  14 TAIWAN
215833.5* 50.989N 178.023W  33N 4.3     1.0  26 ANDREANOF ISLANDS, ALEUTIAN IS.
OCT 04
034912.5  61.359N 150.344W  60*         0.5  12 SOUTHERN ALASKA. ML 3.2 (PMR).
204105.8  39.793N 141.111E 101  4.6     1.0  44 EASTERN HONSHU, JAPAN
222839.6  34.968N 116.956W   5G         0.7  17 SOUTHERN CALIFORNIA. MD 3.1
OCT 05
015154.1? 16.65 N  46.17 W  10G 4.7 4.8 1.0  36 NORTHERN MID-ATLANTIC RIDGE
100625.3  34.395N 116.436W   5G         0.7  15 SOUTHERN CALIFORNIA. MD 3.5
114028.7& 37.457N 118.840W   7               26 CALIFORNIA-NEVADA BORDER REGION.
185901.2  51.663N 179.015E  67D 5.2     1.2  75 RAT ISLANDS, ALEUTIAN ISLANDS.
231601.5  34.353N 116.420W   5G         0.9  13 SOUTHERN CALIFORNIA. MD 3.2
OCT 06
102824.6   5.134S 150.840E  52D 5.8     0.7  60 NEW BRITAIN REGION, P.N.G.
151453.9* 51.062N 177.567W  33N 5.1 4.5 1.2  51 ANDREANOF ISLANDS, ALEUTIAN IS.
153803.9  43.293N  71.571W   5G         1.0  11 VERMONT-NEW HAMPSHIRE REGION.
        mbLg 3.4 (WES). Felt at Franklin and Laconia, New Hampshire.
171908.5  51.203N 177.813W  33N 5.1 5.1 0.9  69 ANDREANOF ISLANDS, ALEUTIAN IS.