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 August 27 - September 2, 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, September 2, 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. Five of these were as large as M2.0. The weekly total compares with 22 earthquakes recorded during the previous 7-day period, only one of which was as large as M2.0. Three of the five M2 events recorded during the week occurred along the San Andreas system; interestingly, all three occurred within an 8-hour period last Sunday. On the peninsula a M2.5 earthquake occurred Sunday morning about 3 miles offshore of Pacifica along one of the splay faults to the San Andreas (#3/1). The Loma Prieta segment experienced a couple of small earthquakes, the largest a M2.0 Sunday afternoon that occurred at it's southern end, about 4 miles northeast of Watsonville (#4/1). The creeping segment of the San Andreas also experienced several small events, capped by a M2.1 event Sunday evening 2 miles southwest of San Juan Bautista (#5/1). Activity was also observed on numerous faults in the East Bay. The central Calaveras produced several small earthquakes, the largest a M2.2 event about 9 miles east of San Jose (#7/1). The Mission fault experienced a M1.9 event early Monday morning (#6/1). The Hayward fault saw two M1 events: a M1.7 last Thursday about 4 miles northeast of San Leandro (#1/1) and a M1.1 early Sunday morning 3 miles northwest of Fremont. At the north end of the Calaveras, near the "step over" to the Concord fault, a M1.9 occurred Tuesday afternoon (#9/1). Monday evening a M1.8 occurred near the Antioch fault about 9 miles northwest of Antioch (#8/1). Finally, a M2.1 event occurred last Thursday in the northern Diablo Range about 12 miles east-southeast of Livermore (#2/1). Northern California There was a noticeable increase in seismicity in northern California during the past week, both in the number of earthquakes larger than M2 and in the number of M3 earthquakes. Three M3 earthquakes occurred along the Mendocino transform fault alone, the most in one week in the Cape Mendocino area since mid-July (#3,#4/2). The only other earthquake of note in this area was a M2.1 event 42 miles northeast of Eureka. The focal depth calculated for this earthquake was 35 km, placing this earthquake below the North American plate, either within the underlying Gorda Plate, or along the interface between the two plates. South of Cape Mendocino, a M2.0 earthquake occurred Saturday evening along the San Andreas near Point Arena (#5/2). Although the San Andreas is generally believed to be "locked" between the Golden Gate and Cape Mendocino, occasional small earthquakes have been observed in this area in the past 30 years, some as large as M3. The most recent activity near Point Arena was a pair of M2 events in April of 1991. East of Point Arena, a handful of M2-3 earthquakes occurred in the central Coast Ranges south and west of Clear Lake. Just after midnight Friday a M2.1 occurred west of the Maacama fault, about 12 miles south of Ukiah. Wednesday morning a pair of M2 earthquakes occurred only a minute apart near the southeast end of Clear Lake, about 17 miles east of Lakeport (#7/2). Finally, Wednesday afternoon a M3.0 earthquake occurred in the Geysers geothermal area (#9/2), the largest earthquake seen here since a M3.1 in mid-June of this year. In the eastern Sierra Nevada the Mono Basin was once again active, producing 7 earthquakes as large as M2, the largest a M3.0 event last Thursday evening that initiated the sequence (#2/2). This activity occurred in the east end of the basin, the same location as the "triggered" earthquakes that followed the M7.5 Landers earthquake in late June. The area had been quiet at the M2 level since early August. To the north, a number of M2 earthquakes occurred in the vicinity of Lake Tahoe including a M2.6 last Thursday that was located directly beneath the lake itself (#1/2). Sunday evening a M3.2 occurred about 6 miles northwest of Truckee (#6/2). Long Valley Caldera Activity also increased noticeably in the Long Valley caldera over that observed during the previous few weeks. A small swarm occurred early in the week in the south moat area, about 1 mile southeast of Mammoth Lakes. It consisted of six M2 events that occurred within an eight-hour period last Friday night (#1/3). The area remained quiet until Tuesday morning when a M2.1 occurred along the southern edge of the caldera 5 miles southeast of Mammoth Lakes (#2/3). Activity south of the caldera was limited with only two M2 earthquakes, both late Wednesday. The first, a M2.4, occurred about one mile northwest of Mt. Morrison (#3/3); the second, a M2.0, occurred beneath Wheeler Crest, near Round Valley Peak (#4/3). USA Seismicity For the second week in a row the National Earthquake Information Service reported a M5.5 in the lower 48 states. But, whereas last week's earthquake occurred offshore of southern Oregon and was barely felt, this week's earthquake occurred in southwestern Utah, produced some damage, and was felt strongly over a wide area (#4/4). The moderate earthquake, occurring early Wednesday morning, produced some damage in the town of Hurricane, Utah and was felt as far away as Las Vegas, Nevada. Rock falls caused by the earthquake closed some roads, including the main road through Zion National Park, which had to close temporarily as a result. Last Friday a M3.9 occurred in eastern Idaho, about 40 miles northeast of Borah Peak (#1/4). It was felt in Arco, Idaho and as far away as Butte, Montana. Sunday evening, a M3.6 occurred in north central Wyoming (#2/4). In southern California aftershocks to the M7.5 Landers earthquake continue to decline. During the past week, only 7 aftershocks as large as M3 were recorded, the largest a M4.2 event early Monday that occurred along the Landers rupture (#3/4). The Planet Earth Two deadly earthquakes occurred during the past week according to information provided by the National Earthquake Information Service. Last Friday a M5.7 earthquake struck western Pakistan killing at least three people in the Kalat area (#1/5). Then Tuesday afternoon a M7.0 earthquake struck about 35 miles off the coast of central Nicaragua (#6/5). Although the shaking from the earthquake was not strong enough to cause serious damage, the tsunami waves generated by the earthquake caused devastation along several hundred miles of the Nicaraguan coast. At least 62 people were reported killed, 227 injured, and approximately 3,000 were still missing from the waves that were estimated to have been as high as 25 feet and that had run-ups of up to 1000 meters in places. Some damage was also reported in Costa Rica. The earthquake was felt throughout most of Nicaragua and as far south as San Jose, Costa Rica. Seven M5 aftershocks occurred in the 18 hours following the mainshock. Earlier in the week, an earthquake of nearly the same magnitude occurred along the mid-Atlantic Ridge, north of Ascension Island (#2/5). Two M6.0 earthquakes occurred along the western Pacific margin, the first last Friday offshore the southeast coast of Honshu, Japan (#3/5), the second on Tuesday beneath the island of Taiwan (#5/5). A M5.1 occurred in the Gobi Desert of southeast Mongolia on Monday (#4/5). 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 AUG 27 1355 3.26 38 40.81 119 38.80 0.06 12 1 .07 1.0 1.3 WAK 2.4 92 AUG 27 2025 15.79 39 6.97 120 1.63 11.12 29 1 .16 1.2 4.0 WAK 2.9 92 AUG 27 2220 49.43 38 44.60 122 42.45 2.79 17 .06 .2 .8 NAP 2.1 92 AUG 28 229 57.44 38 1.34 118 43.75 7.72 26 .16 1.0 5.4 MOL 3.0 92 AUG 28 456 28.90 37 39.03 118 56.35 6.58 19 .12 .4 .7 SMO 2.1 92 AUG 28 457 6.12 37 38.64 118 56.96 6.43 32 .12 .3 .4 SMO 2.9 92 AUG 28 559 17.92 38 1.10 118 43.74 6.81 30 .11 .7 5.6 MOL 2.8 92 AUG 28 634 11.41 37 38.72 118 56.66 6.47 41 .14 .3 .4 SMO 2.1 92 AUG 28 636 34.34 37 38.60 118 56.90 6.45 37 .14 .3 .5 SMO 2.2 92 AUG 28 738 44.75 37 38.70 118 56.79 6.73 40 .13 .3 .4 SMO 2.5 92 AUG 28 1117 52.92 38 1.58 118 43.57 8.40 39 .10 .9 3.2 MOL 2.3 92 AUG 28 1244 43.33 37 38.66 118 56.88 6.63 42 1 .13 .3 .4 SMO 2.7 92 AUG 28 1504 12.31 40 20.02 125 11.07 5.73 19 .25 3.915.1 MEN 2.3 92 AUG 28 1745 7.56 40 17.29 124 21.38 6.96 24 1 .16 .7 .3 MEN 2.7 92 AUG 28 2103 49.48 40 20.77 125 9.05 1.07 25 .20 3.7 6.1 MEN 3.0 92 AUG 29 155 39.19 37 35.03 121 34.78 1.54 50 2 .17 .4 2.3 HAM 2.2 92 AUG 29 248 22.69 38 47.16 122 46.24 3.22 22 .09 .3 .7 GEY 2.3 92 AUG 29 710 41.16 38 58.62 123 10.61 5.75 19 .08 .3 1.7 MAA 2.1 92 AUG 29 756 50.83 39 36.71 119 56.65 6.83 14 1 .18 2.1 2.4 WAK 2.2 92 AUG 29 1111 53.99 40 21.20 125 4.36 9.23 18 .16 4.1 3.2 MEN 2.2 92 AUG 29 1616 35.14 41 1.47 123 25.64 35.15 23 2 .14 .4 1.2 KLA 2.3 92 AUG 29 1843 58.18 38 1.91 118 43.54 7.59 40 1 .11 .9 4.7 MOL- 2.5 92 AUG 29 1933 45.99 40 17.43 124 22.24 14.21 22 1 .14 .6 .3 MEN 2.5 92 AUG 29 2317 35.26 38 2.31 118 43.40 7.22 33 1 .13 1.2 7.3 MOL- 2.3 92 AUG 30 227 7.17 38 51.80 123 41.10 2.58 18 1 .15 1.1 2.0 PAR 2.0 92 AUG 30 1049 12.97 38 48.63 122 48.45 4.60 41 .16 .3 .5 GEY 2.1 92 AUG 30 1517 58.84 39 40.77 120 22.06 14.96 30 1 .13 1.2 3.1 WAK 2.8 92 AUG 30 1623 27.71 37 38.30 122 31.85 0.63 84 .22 .3 1.9 SFP 2.5 92 AUG 30 1721 42.02 36 56.38 121 41.08 12.24 67 1 .12 .2 .4 SJB 2.0 92 AUG 30 1745 7.58 40 17.44 124 21.35 7.31 12 .09 .7 .3 MEN 2.8 92 AUG 30 2342 9.19 39 24.08 120 14.38 15.70 35 1 .17 1.4 2.0 WAK 3.3 92 AUG 31 9 50.23 36 49.71 121 33.56 7.01 52 .20 .3 .6 SJB 2.1 92 AUG 31 39 17.02 40 16.10 124 27.63 30.62 20 1 .12 .8 .6 MEN 2.4 92 AUG 31 1833 49.96 37 22.04 121 43.81 5.88 21 .06 .3 .5 ALU 2.2 92 AUG 31 2303 11.02 36 31.11 121 5.96 10.60 38 3 .08 .2 .5 PIN 2.2 92 SEP 1 1721 56.74 37 37.22 118 53.47 9.87 17 .10 .4 .6 SMO 2.0 92 SEP 1 2058 3.25 36 28.46 121 2.46 1.43 22 .07 .2 1.0 BIT 2.1 92 SEP 2 409 51.16 40 28.81 124 28.37 26.48 21 2 .09 .8 .6 MEN 2.2 92 SEP 2 735 25.20 40 18.46 124 25.33 7.92 25 2 .13 .7 .3 MEN 3.4 92 SEP 2 736 41.36 40 18.38 124 25.18 8.31 26 2 .14 .8 .4 MEN 3.3 92 SEP 2 740 46.68 40 18.49 124 25.21 8.04 19 1 .09 .7 .4 MEN 2.0 92 SEP 2 1755 45.78 38 0.28 118 43.94 7.51 9 .09 1.9 5.6 MOL 2.0 92 SEP 2 1759 57.28 39 0.87 122 35.77 3.69 23 .20 .5 1.7 BAR 2.6 92 SEP 2 1800 54.69 39 1.21 122 35.38 0.10 20 .24 .5 3.6 BAR * 2.4 92 SEP 2 1839 36.23 36 43.92 121 1.06 1.16 70 .27 .4 4.1 ORT * 2.6 92 SEP 2 1918 23.17 39 32.61 121 10.07 9.25 15 .07 .5 1.4 WAK 2.4 92 SEP 2 1934 59.97 40 23.01 124 13.22 9.61 11 .08 .4 .6 MEN 2.1 92 SEP 2 2040 26.72 38 50.04 122 48.41 0.04 35 .25 .4 1.3 GEY * 3.0 92 SEP 2 2102 53.85 37 34.19 118 52.46 6.02 16 .09 .4 .8 MOR 2.4 92 SEP 2 2142 53.79 38 48.82 122 46.48 2.54 15 .12 .4 .7 GEY 2.0 92 SEP 2 2204 18.47 40 28.24 124 41.87 30.30 8 .09 4.9 2.3 MEN 2.2 92 SEP 2 2303 23.45 37 58.76 118 41.08 4.96 14 .08 1.4 2.7 MOL 2.0 92 SEP 3 302 43.97 37 27.09 118 41.20 5.28 26 .08 .4 1.5 WCS 2.0 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. 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 --------------------------------------------------------------------------- AUG 27 081136.7* 17.603N 101.336W 33N 4.2 0.8 22 NEAR COAST OF GUERRERO, MEXICO 122856.9 38.669N 142.236E 45 4.6 1.0 26 NEAR EAST COAST OF HONSHU, JAPAN 153714.3* 54.506N 166.459E 33N 4.4 0.6 27 KOMANDORSKY ISLANDS REGION 162816.4* 54.455N 166.473E 33N 4.4 1.1 20 KOMANDORSKY ISLANDS REGION 180412.9? 9.70 N 126.52 E 150? 4.2 1.7 11 MINDANAO, PHILIPPINE ISLANDS AUG 28 005054.2 29.130N 66.792E 33N 5.7 5.6 1.1 59 PAKISTAN. At least three people killed in the Kalat area. Felt at Khuzdar, Manguchar, Mastung & Quetta 084041.9* 23.599S 179.052E 550G 4.6 0.8 38 SOUTH OF FIJI ISLANDS 095124.1* 12.394N 89.479W 24D 5.1 4.2 0.9 63 OFF COAST OF CENTRAL AMERICA 152616.3 44.578N 113.336W 5G 0.8 37 EASTERN IDAHO. ML 3.9 (GS). Felt at Arco. Felt slightly at Butte, Montana. 171506.3* 22.016S 179.621W 596D 5.0 0.9 50 SOUTH OF FIJI ISLANDS 181845.6 0.906S 13.658W 10G 6.5 6.9 1.0 131 NORTH OF ASCENSION ISLAND. AUG 29 131037.8 54.442N 166.508E 37D 5.0 4.8 0.9 68 KOMANDORSKY ISLANDS REGION 132002.7 54.458N 166.515E 33N 4.7 0.8 34 KOMANDORSKY ISLANDS REGION 150905.9 54.578N 166.431E 33N 4.6 4.1 1.0 37 KOMANDORSKY ISLANDS REGION 191907.3 33.227N 137.990E 307D 6.0 0.7 123 NEAR S. COAST OF HONSHU, JAPAN. 204559.8 60.782N 151.066W 78* 1.1 15 KENAI PENINSULA, ALASKA AUG 30 030814.1 58.424N 151.422W 33N 1.1 17 KODIAK ISLAND REGION. ML 4.3 073228.8* 54.681N 166.357E 33N 4.4 0.6 17 KOMANDORSKY ISLANDS REGION 081512.0 33.999N 118.375W 14 0.7 35 SOUTHERN CALIFORNIA. ML 3.3 (GS). Felt in the Los Angeles area. 112521.4* 15.154S 173.720W 48D 5.0 5.1 0.6 28 TONGA ISLANDS 135113.3 64.829N 165.684W 18D 4.4 1.0 37 NORTHERN ALASKA. ML 4.7 (AEIC). Felt at Nome. 200907.5 17.586S 178.765W 574D 5.9 0.8 101 FIJI ISLANDS REGION. AUG 31 014014.7* 43.776N 107.028W 5G 0.8 10 WYOMING. ML 3.6 (GS). 043956.1* 11.394S 118.259E 33N 5.4 4.7 1.5 19 SOUTH OF SUMBAWA, INDONESIA 054436.0* 54.663N 166.280E 33N 4.5 0.8 22 KOMANDORSKY ISLANDS REGION 072554.3 43.903N 106.956E 33N 5.1 4.8 0.9 49 MONGOLIA 092538.1 34.474N 116.445W 5G 0.8 17 SOUTHERN CALIFORNIA. MD 4.2 161910.0 27.222N 142.538E 33N 4.8 0.7 32 BONIN ISLANDS REGION 194223.1* 20.800N 94.446W 10G 4.2 1.1 20 BAY OF CAMPECHE SEP 01 121723.8 34.587N 116.359W 5G 0.9 20 SOUTHERN CALIFORNIA. MD 3.7 164111.1 23.746N 121.506E 33N 6.0 5.4 0.8 51 TAIWAN 211757.0 34.244N 116.765W 5G 0.8 9 SOUTHERN CALIFORNIA. MD 2.9 SEP 02 001600.9 11.808N 87.354W 33N 5.4 7.0 1.1 75 NEAR COAST OF NICARAGUA. Mo=3.2*10**20 Nm (PPT). At least 62 people killed, 227 injured and 3,000 missing in Nicaragua. At least 600 houses destroyed along the west coast of Nicaragua. Some damage also reported in Costa Rica. Most of the casualties and damage are believed to be caused by a tsunami affecting the west coasts of Nicaragua and Costa Rica, reaching heights up to 8 meters. Tsunami run-up of 1000 meters was reported at Masachapa, where at least 15 people were killed. Felt in Chinandega and Leon Departments, Nicaragua. Also felt at El Crucero, Managua and San Marcos, Nicaragua and at San Jose, Costa Rica. 002103.7* 10.529N 87.207W 33N 5.7 0.9 52 OFF COAST OF COSTA RICA 002827.9? 11.64 N 87.49 W 33N 5.2 1.0 22 NEAR COAST OF NICARAGUA 003101.2? 11.70 N 88.16 W 33N 5.4 1.0 28 OFF COAST OF CENTRAL AMERICA 005733.8* 11.063N 87.595W 33N 5.3 0.9 51 NEAR COAST OF NICARAGUA 014241.3* 11.695N 87.920W 33N 5.4 1.0 64 NEAR COAST OF NICARAGUA 055002.7* 5.943S 112.266E 635D 5.9 0.7 21 JAVA SEA 102619 Q 37.0 N 113.5 W 10G 5.5 0.8 54 UTAH 165045 Q 10.1 N 86.5 W 33N 5.5 1.0 62 OFF COAST OF COSTA RICA 182857 Q 11.0 N 86.8 W 33N 5.5 1.2 67 OFF COAST OF COSTA RICA