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).