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.

Special note: the section on the Cape Mendocino Earthquakes
do contain estimates of future earthquake hazards.

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
                            April 23 - 29, 1992
                                     
                         Data and text prepared by
                    David Oppenheimer, Paul Reasenberg,
     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

                     *********************************
                          SPECIAL SECTION ON THE 
                      CAPE MENDOCINO EARTHQUAKE SWARM
                                -----------
                          Regular Sections follow
                     ********************************

 THE CAPE MENDOCINO EARTHQUAKES

   On April 25 and April 26 three powerful earthquakes rocked the Cape
Mendocino, California area (Fig. 1). Injuries and significant damage
occurred in the nearby towns of Ferndale, Petrolia, Fortuna, Rio Del, and
Scotia, and the earthquakes were felt as far north as southern Oregon and
over much of northern California. The first earthquake had a magnitude (M)
of 6.9 and occurred at 11:06 PDT (18:06 UTC) beneath the town of Petrolia
at a depth of abut 15 km (10 miles).  A Magnitude 6.2 aftershock occurred
on April 26 at 00:07 PDT and this was followed at 04:18 PDT by another
earthquake of Magnitude 6.5 that caused additional extensive damage.  These
aftershocks occurred more than 11 miles out to sea at depths of 12 and 14
miles, respectively.  As of 9 a.m. PDT on April 30, over 1000 aftershocks
were recorded by the seismographic network of the U.S. Geological Survey. 
Most of the aftershocks are located offshore within a trapezoidal region 10
to 13 miles on a side, north of the Mendocino Fracture Zone.

PREVIOUS LARGE EARTHQUAKES IN AREA

   Last weekend's earthquakes occurred in one of the most seismically
active areas in California. Since the 1870's, 15 earthquakes with Magnitude
6 and larger have occurred in the vicinity of the Mendocino Fracture Zone. 
The largest of the historic earthquakes in this area, a Magnitude 7.2
earthquake, occurred on January 22, 1923. In addition, a Magnitude 6.9
earthquake occurred on November 11, 1980 about 45 miles north, beneath the
ocean west of Eureka.  Most recently, a Magnitude 6.0 earthquake occurred
on August 17, 1991 about 13 miles southeast of Cape Mendocino, near the
town of Honeydew.

REGIONAL EARTHQUAKE HAZARD AND PLATE MOTIONS

   The area of last weekend's earthquakes is one of the most geologically
complex areas in California.  Three major faults -- the San Andreas, the
Mendocino fracture zone, and the southern end of the Cascade subduction
zone -- all meet here. These faults define and separate three major plates
of the Earth's surface: the Pacific plate, the Gorda plate and the North
American plate. The point where these plates and faults come together is
called a "triple junction".  Because a triple junction has to accommodate
plate motion in several directions, its faulting is varied and its
seismicity is high. Unlike strike slip faults such as the San Andreas,
whose horizontal movements on a nearly vertical plane are easily
accommodated over long time periods, a triple junction's geometry makes it
inherently unstable, and requires that it change with time. Because much of
this area lies under the Pacific Ocean, relatively little is known about
the details of the geology here.

AFTERSHOCK HAZARD FORECAST

   Virtually all earthquakes produce aftershocks, and last Saturday's event
has already produced two strong ones. A strong aftershock poses additional
hazard, particularly to those people in and near structures already damaged
in last weekend's earthquakes. The probability for aftershocks decreases
with time most rapidly during the first week after the mainshock. But it is
not uncommon for a strong aftershock to occur several weeks or months after
a mainshock.  To assess the chances for additional damaging aftershocks,
scientists at the U.S. Geological Survey rely on the typical behavior of
past California sequences and on the behavior of the aftershocks in the
current sequence that have occurred so far. From these observations we have
estimated the chance of additional strong aftershocks as follows: 

   In the 30 day period beginning 9 p.m., Wednesday 29 April, there is a
"small but not negligible chance" (about 10 percent) of at least one
additional Magnitude 6 or larger aftershock.

   In the 30 day period beginning 9 p.m., Wednesday 29 April, there is a
"good chance" (about 50 percent) of at least one additional Magnitude 5 or
larger aftershock. A Magnitude 5 or larger aftershock is considered capable
of producing additional damage.

HAZARD FROM NEARBY CASCADE SUBDUCTION ZONE

   From the Mendocino triple junction, the Cascade subduction zone extends
approximately 750 miles north to the Canadian border and is the first of a
string of subduction zones to ring the Northern Pacific.  Downward and
eastward motion of the Gorda plate along this subduction zone, beginning at
least 6 million years ago and continuing today, produced the volcanic
Cascade Range in Washington, Oregon, and northern California. The volcanoes
in this range, such as Mount St. Helens and Mount Lassen, remain active
today. Other subduction zones ringing the Pacific Ocean have produced great
earthquakes in recent times, including the Alaska earthquake of 1964
(Magnitude 8.5) and the Chile earthquake of 1960 (Magnitude 9.5). The
Cascade subduction zone is believed to be capable of producing a Magnitude
8 to 9 earthquake. Great earthquakes there may occur as often as every 300
or 400 years, on average. There is good evidence that the last great
earthquake on the Cascade subduction zone occurred about 300 years ago. 
The probability of such an earthquake occurring in the next few decades has
not been estimated, however.

ADDITIONAL LARGE EARTHQUAKES

   While little can be said to specifically relate last weekend's
earthquakes to the possibility of an additional large earthquake in the
area, scientists note a general tendency for large earthquakes to cluster
-- that is, the occurrence of one earthquake in a region may increase the
chances for another. Because of the historical seismic activity in the
region of last weekend's earthquakes, the occurrence of another large
earthquake there is possible. One seismologist summed it up this way: "The
northern California coast, from Cape Mendocino north, is earthquake
country, and no less so than southern California and the Bay area. It has
been in the past, it was this week, and it continues to be."

POSSIBILITY OF TSUNAMI

   When an earthquake occurs beneath the ocean, an additional hazard is
presented to the population living along the coast. A tsunami, or large
sea wave, may be produced by movement of the ocean floor resulting from
the earthquake. A tsunami can be produced by either nearby or distant
earthquakes. In 1964, the harbor area at Crescent City, Ca., was severely
damaged by a tsunami produced by the great Alaska earthquake, some 1500
miles away.  Last Saturday's earthquake produced a small tsunami measuring
about 3 feet at Crescent City, about 0.6 feet at Point Arena, and about 0.3
feet in Hawaii. At least two great earthquakes with epicenters on land have
been followed by tsunamis on the nearest coast (Chile, 1922; Turkey, 1939). 
The tsunami may reach the nearest coast a few minutes to some hours after
the earthquake.
   Tsunamis on the California coast are rare. However, on November 4, 1927,
a shock of magnitude 7.4 sent in a wave 5 to 7 feet high along the coast
north of Point Arguello.

WHAT TO DO IF YOU EXPERIENCE STRONG SHAKING NEAR THE COAST

   Tsunamis rarely exceed 20 to 30 feet in height. A resident of a coastal
area who experiences severe ground shaking lasting 15 seconds or longer
should assume that an earthquake has occurred and that a tsunami may
follow. Immediate evacuation to upland locations, at least 100 feet
above sea level, would be advised.
   Another warning sign of impending tsunami wave is the withdrawing of
water from harbors and beaches. A sudden and unusually low "tide" may
precede a tsunami wave. A resident of a coastal area who notices such
an unusual and sudden withdrawal of the sea should assume that a tsunami
wave may follow within a few minutes, and immediately evacuate to
higher ground.

TECHNICAL DESCRIPTION OF THE EARTHQUAKES

   Preliminary analysis of last weekend's earthquakes by scientists at the
U. S. Geological Survey and the California Institute of Technology
indicates that the main shock probably occurred on a fault between the
Gorda and North American Plates. Centroid moment tensor (CMT) solutions of
teleseismic waveforms indicate that the main shock was a reverse mechanism
with strike trending about N 32-45 degrees W, and with the fault plane
dipping either 68 degrees southwest or 28 degrees northeast. The latter
plane is considered more likely for the following reasons.  Most
aftershocks are shallower than the main shock hypocenter and are located
out to sea, suggesting that the main earthquake rupture propagated upward
as it advanced seaward.  Neither surface rupture nor a zone of concentrated
deformation on land, as might be expected for the southwest-dipping plane,
has yet been found. Preliminary aftershock locations also image a northeast
dipping plane.  In addition, a tsunami, recorded after the main shock in
northern California, Oregon and Hawaii, suggests submarine surface
deformation or possible rupture of the sea floor. If slip occurred on the
northeast dipping plane, then this earthquake may be the first recorded
earthquake to rupture a portion of the Cascadia megathrust. However, the
Mendocino fracture zone is a very complex region and the main shock may
also have ruptured one of the active thrust faults within the North
American plate that can be observed at the surface.
   The CMT solutions for the two large aftershocks indicate either
left-lateral motion on northeast trending vertical faults or right-lateral
motion on northwest trending vertical faults.  Because of their depth and
location at sea, these earthquakes are believed to have occurred within the
Gorda plate. Although these earthquakes occurred on faults that were
distinct from the fault ruptured by the main shock rupture, they are still
considered to be aftershocks because they occurred near and soon after the
main shock.  The Magnitude 6.5 aftershock was notable in that seismograms
recorded worldwide were enriched in frequencies from 1 to 5 Hz, relative to
those of the main shock.  This suggests that the seismic source processes
for the two events differed greatly.  While many buildings were undoubtedly
weakened by the main shock, the Magnitude 6.5 aftershock may have
contributed more to the damage because buildings are more susceptible to
shaking at these higher frequencies.  Rupture directivity may also account
for variations in damage caused by the two earthquakes.

STRONG GROUND MOTION RECORDING OF THE EARTHQUAKE

   The California Division of Mines and Geology recovered strong ground
motion recordings from the epicentral region and reported that a
seismograph located at Cape Mendocino recorded peak accelerations
exceeding 2 g for about 7 seconds. (One "g" is the acceleration due to
the Earth's gravity).  This value is the highest earthquake acceleration
ever recorded in California and will undoubtedly be the subject of intense
study. This observation has implications for building design and
theoretical models of earthquake rupture.  At Petrolia, 5 km from the
epicenter, the acceleration was 0.69 g, and on a bridge at Rio Dell the
peak acceleration was 1.2 g. The two large aftershocks produced ground
accelerations of 0.60 g and 0.57 g at Petrolia.

San Francisco Bay Area
       
      With all the seismicity in both northern and southern California
during the past week, it is reassuring to see that there was little or no
change in activity in the Bay Area.  For the 7-day period ending at
midnight on Wednesday, April 29, 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.  Seven of these were as large
as M2.0, including one M3 event on the central Calaveras fault, about 10
miles east of San Jose (#1 in fig. 2).  This compares with 17 earthquakes
recorded during the previous 7-day period, four of which were as large as
M2.0. 
   The M3.0 earthquake on the Calaveras was part of a sequence of small
earthquakes that occurred last Thursday afternoon.  It included two other
events that were as large as M2.  On Sunday two more M2 events occurred
about 8 miles northeast of San Jose, also along the Calaveras (#3/2). 
This central part of the Calaveras fault is one of the most seismically
active areas in the East Bay, producing numerous M1-M3 events, almost
on a weekly basis.  
    The only other earthquakes of note were a M2.0 event on the Black
Mountain fault, about 9 miles southwest of San Jose (#2/2), and a M2.5
event one mile south of Pacifica on a small splay fault of the San Andreas
(#4/2).  This splay fault has experienced several small earthquakes in the
past month, including another M2.5 on April 10 and a M1.9 on April 6.       
[NOTE:  The Pacifica earthquake was initially reported as a M3.4
earthquake.  This happened because a true M3.4 earthquake occurred
almost simultaneously at Coalinga in central California.  Readings from
this earthquake were mingled with those of the Pacifica event leading to
the mistaken magnitude measurement.]  
   
Northern California
    
   Aside from the major earthquake sequence at Cape Mendocino, discussed
above, seismicity in the rest of the state remained at normal levels.  The
only other earthquakes in northern California worth mentioning were a M2.2
event north of Clear Lake Saturday afternoon (#3/3) and a M2.7 event
southeast of Redding Wednesday morning (#7/3).  A felt earthquake occurred
Tuesday morning in the northeastern Sierra-Nevada about 16 miles southeast
of Markleeville (#5/3).  This M3.6 was followed seven minutes later by a
M2.9 aftershock.
   In central California the only earthquakes of any consequence were two
events about 22 miles north of Coalinga early Tuesday evening (#6/3).  The
largest of these was a M3.4 event that was followed 3 minutes later by a
M2.3 aftershock.
  
Long Valley Caldera

    Three earthquakes as large as M2 occurred within the Long Valley
caldera during the week.  The first of these, a M2.1 event, occurred just
after noon on Tuesday at the east end of the south moat area (#2/4).  A
M2.4 event followed about 14 hours later in the central part of the south
moat (#3/4).  Late Wednesday evening, a M2.4 occurred along the southwest
side of the resurgent dome and was accompanied by several smaller events
(#4/4).     
USA Seismicity
 
   Outside of California, no earthquakes were located in the lower 48
states during the past week by the National Earthquake Information Center.
     
The Planet Earth

   While the M6.9 northern California earthquake was the largest event on
the planet, several other potentially damaging earthquakes were recorded
during the past week.  Two of these occurred in the Himalayan front where
the Indian plate is colliding with the Eurasian plate.  First was a pair of
M6 events last Thursday that struck along Myanmar's (Burma's) eastern
border with China (#1/5).  The following day a M6.3 earthquake struck
central Pakistan (#3/5).  
   Other earthquakes of note include a pair of M4 events in south-central
Alaska (#2/5), a M4.8 in central Iceland (#4/5), a M4.8 beneath the
northeast coast of Sicily (#5/5), and a M5.4 near the western border of
Nicaragua and Costa Rica (#6/5).

              Table 1.  Central California Seismicity (M>2.0)
                (only Mendocino events > M4.0 are included)

--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 APR 23 1258 38.14 39 42.70 123  9.14  0.02 20   .31  .618.8 BARB  2.0
92 APR 23 1920 25.66 39 23.92 119 56.25  5.39 16   .16 3.7 9.8 WAKW  2.8
92 APR 23 2302 38.75 37 20.87 121 42.66  7.67107   .17  .2  .5 ALUA  3.0
92 APR 23 2307 20.40 37 20.77 121 42.50  7.01 48   .09  .2  .4 ALUA  2.0
92 APR 23 2310 57.21 37 20.74 121 42.47  7.38 52   .11  .2  .5 ALUA  2.2
92 APR 24 1126 12.40 35 43.42 118  3.80  6.56  9   .09  .6 1.9 WWFW  2.0
92 APR 24 2320  2.08 38 49.12 122 46.67  0.89 16   .09  .2  .5 GEYG  2.1
92 APR 25 1010 16.25 37 34.52 118 26.84  8.25 26   .09  .3  .7 CHVC  2.1
92 APR 25 1806  4.21 40 22.08 124 18.95 15.07  8   .16 1.1  .8 MENM  6.9
92 APR 25 1820 14.52 40 27.57 124 22.33  9.30 12   .13 1.9 4.0 MENM  4.5
92 APR 25 1828 57.25 40 21.75 124 28.47 10.22 13   .10 3.3 2.5 MENM  4.1
92 APR 25 1831 50.32 40 18.83 124 35.05  1.25 18   .24 3.8 6.6 MENM  4.3
92 APR 25 1842 14.11 40 18.27 124 33.00  0.07 12   .15 2.6 4.2 MENM  4.0
92 APR 25 1847  3.93 40 18.95 124 28.53  0.08 13   .24 3.8 6.5 MENM  4.5
92 APR 25 1914 52.05 40 18.57 124 31.93  4.80 13   .10 2.2 2.2 MENM  4.7
92 APR 25 1941 59.22 40 19.83 124 25.42  6.60 19   .20 1.7  .6 MENM  4.1
92 APR 25 1950 42.11 40 18.33 124 26.29  5.60 14   .09 1.3 1.0 MENM  4.0
92 APR 25 2225 25.61 40 19.39 124 26.34  6.84 17   .17 1.3  .5 MENM  4.0
92 APR 25 2243 39.23 39 18.87 122 47.83  5.00 14   .07  .410.1 BARB  2.2
92 APR 26  100 58.14 40 22.04 124 29.52  6.40 14   .13 1.6  .5 MENM  4.1
92 APR 26  412 21.58 37 16.33 122  1.94  4.21 49   .16  .3  .5 BLMB  2.0
92 APR 26  741 39.73 40 24.91 124 36.15 20.29 11   .12 2.2  .6 MENM  6.0
92 APR 26 1118 25.79 40 22.69 124 34.50 22.23 13   .13 2.0  .6 MENM  6.5
92 APR 26 1129  8.00 40 27.25 124 34.89 12.53  8   .11 1.7 2.0 MENM  4.0
92 APR 26 1204 29.85 40 24.49 124 25.64 11.00 20   .11  .9  .3 MENM  4.1
92 APR 26 1917  9.70 37 24.10 121 45.92  3.28 71   .13  .2  .6 ALUA  2.2
92 APR 26 2118  4.31 40 24.35 124 36.91 13.42 40   .21 1.218.1 MENM  4.0
92 APR 26 2225 53.32 40 19.09 124 31.61  9.64 10   .08 1.4  .4 MENM  4.2
92 APR 26 2312 27.82 37 25.67 121 46.35  8.88 70   .15  .2  .6 ALUA  2.0
92 APR 26 2339 14.89 40 17.62 124 40.50  4.23  8   .12 8.5 5.3 MENM  4.1
92 APR 27  228 16.34 40 19.89 124 42.31  0.02 11   .10 3.9 6.5 MENM  4.1
92 APR 27  247 20.70 40 20.56 124 44.65  7.18 10   .09 5.8 3.5 MENM  4.4
92 APR 27  308 53.88 38 48.51 122 48.42  4.76 23   .09  .3  .6 GEYG  2.0
92 APR 28 1033 25.42 37 31.10 118 25.39  8.42 20   .09  .3  .8 CHVC  2.1
92 APR 28 1707 18.82 40  1.79 123 46.91 13.94 19   .20  .7  .9 MAAM  2.5
92 APR 28 1713  1.04 40  2.03 123 46.68 12.80 16   .21  .7 1.4 MAAM  2.3
92 APR 28 1723  0.90 38 33.57 119 32.61  7.25 28   .21  .9 9.3 WAKW  3.6
92 APR 28 1730 38.73 38 33.37 119 32.57  4.92 15   .23 1.316.1 WAKW  2.9
92 APR 28 1949 12.54 37 37.43 118 51.77  5.62 17   .09  .3  .4 SMOS  2.1
92 APR 28 2324 26.95 40  2.26 123 46.76 15.60 15   .11  .4  .7 MAAM  2.1
92 APR 29  116 45.00 37 37.65 122 28.93  6.25 72   .20  .3  .5 SFPS  2.5
92 APR 29  117  4.14 36 27.33 120 22.33  9.63 53   .18  .4  .7 COAC  3.4
92 APR 29  120 20.04 36 27.47 120 22.62  7.40 28   .15  .5  .7 COAC  2.3
92 APR 29  932 10.38 37 38.73 118 54.80  5.64 26   .14  .3  .5 SMOS  2.4 
92 APR 29 1555  1.44 40 30.06 122 18.71 21.55 17   .23  .6 1.8 SHAS  2.7
92 APR 29 2204  9.68 36 28.30 121  2.77  5.51 36   .08  .3  .6 BITB  2.1
92 APR 30   54 27.91 37  7.89 121 31.82  7.48 76   .11  .2  .4 CYNC  2.1
92 APR 30  309  1.33 37 39.95 118 54.01  0.49  8   .12  .5  .7 DOMD  2.4

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.  Worldwide Seismicity
         Data from the USGS National Earthquake Information Center

UTC TIME    LAT     LONG    DEP GS MAGS  SD STA  REGION AND COMMENTS
HRMNSEC                         MB  Msz     USED
------------------------------------------------------------------------------
APR 23
122116.5  29.410N 131.417E  33N 5.8 5.1 1.0  84 SOUTHEAST OF RYUKYU ISLANDS
141838.4  22.365N  98.819E  33N 5.7 6.1 1.1 117 MYANMAR-CHINA BORDER REGION.
153252.6  22.359N  98.841E  33N 5.9 6.3 1.1 121 MYANMAR-CHINA BORDER REGION.
                                                Felt at Bangkok, Thailand. 
194857.2  62.562N 150.821W  86D 4.8     1.3  42 CENTRAL ALASKA. Felt at
                                                Anchorage, Palmer, Talkeena and
                                                Wasilla.
APR 24
070727.5* 27.945N  65.935E  33N 5.7 6.3 0.8  25 PAKISTAN
123605.8  33.960N 116.392W  10G 4.3     0.8  25 SOUTHERN CALIFORNIA. ML 4.1
125153.7*  8.626N 140.880E  33N 5.5 5.0 1.0  41 WESTERN CAROLINE ISLANDS
173849.5*  9.539S 109.558W  10G 5.2 5.6 0.8  53 CENTRAL EAST PACIFIC RISE
APR 25
064843.7  64.743N  17.476W  10G 4.8     0.9  28 ICELAND
124616.4  38.483N  15.073E 246D 4.8     0.6  63 SICILY
150220.5* 51.304N 177.827E  33N 4.8     1.2  27 RAT ISLANDS, ALEUTIAN ISLANDS
180604.1  40.297N 124.048W  15G 6.1 6.9 1.4 100 NEAR COAST OF NORTHERN CALIF.
        Forty five people injured and considerable damage in southwestern
        Humboldt County including the towns of Ferndale, Fortuna and Petrolia.
        The preliminary estimate of damage in the area is 3.5 million dollars.
        The earthquake was felt throughout much of northern California as far
        south as San Francisco and southeast to Carson City and Reno, Nevada.
        The earthquake was also felt in many areas of southern Oregon.
APR 26
074138.9  40.309N 124.375W  15G 5.9     0.9  56 NEAR COAST OF NORTHERN CALIF. Ms
        6.0 (GS). This earthquake caused additional damage in the Ferndale and
        Fortuna areas. A fire caused by a broken gas main destroyed much of
        downtown Scotia.
111825.8  40.384N 124.308W  25G 6.0     1.0  77 NEAR COAST OF NORTHERN CALIF. Ms
                                                6.5 (GS). Additional damage in
                                                the Ferndale-Fortuna area.
233916.9  40.177N 124.443W  15G 4.2     1.1  22 NEAR COAST OF NORTHERN CALIF. ML
                                                4.1 (GS).
APR 27
022817.9  40.208N 124.581W  15G 4.5     1.0  32 NEAR COAST OF NORTHERN CALIF.
                                                Felt at Eureka and Fortuna.
024721.9* 40.193N 124.541W  15G 4.7 4.7 1.0  33 NEAR COAST OF NORTHERN CALIF.
082949.0* 11.573N  87.068W  78D 5.4     1.0  63 NEAR COAST OF NICARAGUA. Felt at
                                                Managua.
213107.5  61.947N 154.317W  10G 4.4     1.1  24 SOUTHERN ALASKA. Felt at
                                                McGrath.
APR 29
092542  Q 10.7  S 165.7  E  33N     5.7 1.0  50 SANTA CRUZ ISLANDS