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 January 14 - 20, 1993 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, January 20, 1993 the U.S. Geological Survey office in Menlo Park recorded 32 earthquakes of magnitude one (M1) and greater within the San Francisco Bay area shown in Figure 1. This included a M5.0 event on the Calaveras, the largest Bay Area earthquake since a pair of M5 Loma Prieta aftershocks occurred east of Watsonville in April, 1990. We recorded a M3 on the northern Hayward fault and a fairly active sequence on the San Andreas just southwest of San Juan Bautista that produced six M2 earthquakes. This total compares to 22 earthquakes that were recorded during the previous 7-day period, four of which were as large as M2. The Calaveras earthquake occurred Friday night about 6 miles east- northeast of Gilroy (#3 in Fig.1). It was felt as far away as Sacramento, Monterey, and Modesto, as well as throughout the Bay Area. The earthquake produced no injuries and little or no damage according to press reports. It was not preceded by any foreshocks and produced very few aftershocks. Of the three aftershocks recorded in the first two hours after the earthquake, only one was as large as M1. Ten more aftershocks were recorded during the next five days, the largest a M2.4 early Wednesday morning. This was the largest earthquake on the Calaveras fault since a M5.0 event occurred in the Alum Rock area on April 3, 1989 . It was significant to seismologists because it occurred along one of two zones considered "to be the most likely sites for the next M > 5 earthquakes". This earthquake "forecast" was included in an article published in 1990 in the Journal of Geophysical Research (Vol. 95, No. B6) by Oppenheimer, Bakun, and Lindh. They observed that gaps in M < 3 seismicity coincided with regions of the fault which ruptured during mainshocks. One such gap existed at the site of the January 15 event, which was also the site of a similarly sized earthquake in March, 1949. Based on the elapsed time since that earthquake and the rate of movement on the Calaveras fault, they speculated that this would be a likely site for the next M > 5 earthquake on the fault. Other earthquakes of interest include a M3.0 last Friday morning on the northern Hayward fault, about 2 miles north of Berkeley (#1/1). Although the Hayward is generally quiet, this is one of several zones on the fault that experience occasional earthquakes, some as large as M4. The most recent earthquake of comparable size in this area was a M3.2 on December 13, 1991. The San Andreas fault was also quiet, with the exception of a cluster of M2 events on the creeping segment southwest of San Juan Bautista (#4/1). Between Saturday morning and Monday evening, a total of nine earthquakes > M1 occurred here; six of these were as large as M2. This is the same zone that was active in early December of last year. Northern California Northern California experienced quite a number of M2-3 earthquakes, both along the San Andreas/Coast Range faults and in the northern Sierra Nevada area. This is in contrast to both central California, which experienced only one M2 earthquake (a M2.4 that occurred along the coast about 8 miles northwest of San Simeon (#2/2)), and eastern California, where the only notable earthquake was a M3.1 about 30 miles south of Lone Pine. In northern California, the San Andreas was active near Point Arena, where a M2.3 occurred early Saturday morning (#4/2), and in the Cape Mendocino area, where three M3 earthquakes occurred during the week (#3/2). The adjacent Maacama fault was also active, both at it's northern end with a pair of M2 events (#8/2) and at it's southern end where a M2.2 event occurred about 3 miles northeast of Cloverdale. The Geysers area, just east of the latter "Cloverdale" event, was also slightly more active than normal, producing two M3.5 events late Monday afternoon (#9/2). Finally, a M2.7 occurred north of Clear Lake, near Lake Pilsbury (#5/2). The northern Sierra Nevada produced several notable earthquakes, the largest a M3.2 Saturday evening about 7 miles east of Quincy (#7/2). A M2.8 occurred about this same time northeast of Red Bluff and was followed by two more M2 events in the next three days (#6/2). Other M2 earthquakes include a M2.2 11 miles southeast of Red Bluff, a M2.1 south of Lake Almanor, and a M2.5 13 miles northwest of Truckee (#1/2). Long Valley Caldera There were numerous M1+ earthquakes in the south moat area during the week, most in the western end just southeast of Mammoth Lakes. However, only one earthquake was as large as M2, a M2.2 event that occurred last Thursday morning near the northern end of the Hilton Creek fault (#1/3). Activity south of the caldera was also limited to events smaller than M2. USA Seismicity According to information provided by the National Earthquake Information Service, there were several earthquakes of note in the lower 48 states, in addition to those in California. The first of these was a M3.1 last Thursday that occurred in northern Oklahoma, near the Nebraska border (#1/4). This small earthquake was felt in the Oklahoma towns of Cherokee, Helena, Jet, and Nash. Later the same day another M3.1 occurred in southeastern Tennessee (#2/4); it was felt in the Chattanooga-Cleveland area and also across the border in northern Georgia. Last Friday morning a M4.2 occurred in central Nevada, west of the town of Eureka (#3/4). Just after midnight on Saturday a M4.0 earthquake occurred in the central Gorda plate, off the southern coast of Oregon (#4/4). Finally, a pair of M3 earthquakes were recorded in southern California, aftershocks to the M7.5 Landers earthquake of June, 1992. The Planet Earth The largest and most damaging earthquake during the past week occurred in the Hokkaido, Japan region (#1/5). This Mb6.9 event killed one person and injured at least 364 other with damage at Kushiro, Hokkaido, and Hachinohe, Honshu. Later in the week, a Mb6.0 earthquake occurred beneath the Sea of Japan (#5/5). Other notable earthquakes in the southwest Pacific include a Mb5.8 in the Mariana Islands (#3/5) and a Mb6.2 beneath the Indonesian Island of Sumatera (#6/5). A Mb5.7 occurred in central Xijang (Tibet) that was felt at Lhasa (#4/5). In the western hemisphere there was a Mb4.4 in the Virgin Islands, a Mb4.9 near the coast of Nicaragua, and a Mb4.3 in central Alaska that was felt at Fairbanks (#2/5). 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 93 JAN 14 1242 38.40 39 27.25 120 21.17 10.64 10 .07 3.0 3.5 WAK 2.5 93 JAN 14 1817 22.04 37 36.87 118 48.86 5.04 29 .15 .4 .6 HCF 2.2 93 JAN 14 1959 11.53 35 43.06 121 18.25 9.51 35 .14 .7 1.1 SSM 2.4 93 JAN 15 557 0.19 40 25.42 124 25.49 11.86 12 .09 1.4 .4 MEN 3.0 93 JAN 15 1113 49.15 37 54.77 122 17.19 6.57 82 .17 .2 .5 HAY 3.0 93 JAN 16 629 35.07 37 1.14 121 27.74 7.28103 .14 .2 .4 CYS 5.0 93 JAN 16 1036 49.11 38 50.61 123 39.20 0.07 9 .09 1.6 4.4 PAR * 2.3 93 JAN 16 1704 52.38 36 50.20 121 34.53 7.81 74 .21 .3 .6 SJB 2.5 93 JAN 16 1706 16.72 36 50.12 121 34.51 7.83 63 .20 .3 .6 SJB 2.3 93 JAN 16 1909 13.83 39 22.58 122 52.46 5.83 30 .17 .4 1.7 BAR 2.7 93 JAN 17 137 34.28 38 46.59 122 45.19 0.07 16 .06 .2 .7 GEY * 2.3 93 JAN 17 137 46.47 40 22.50 122 5.67 14.36 7 .08 .8 3.3 SHA 2.8 93 JAN 17 300 26.36 39 57.06 120 48.33 0.96 29 .16 1.111.3 WAK - 3.2 93 JAN 17 558 4.29 36 49.84 121 34.01 7.59 62 .22 .3 .7 SJB 2.2 93 JAN 17 1115 7.82 38 49.04 122 46.01 3.04 22 .11 .3 .7 GEY 2.4 93 JAN 17 1541 48.17 36 50.12 121 34.66 8.52 80 .20 .3 .5 SJB 2.9 93 JAN 17 1716 57.99 36 49.97 121 34.19 7.91 57 .23 .4 .6 SJB 2.3 93 JAN 17 1731 53.42 38 50.30 122 49.18 2.83 17 .09 .3 .9 GEY 2.2 93 JAN 17 1752 0.68 36 49.84 121 34.05 7.47 63 .21 .3 .6 SJB 2.6 93 JAN 17 2204 39.35 40 23.43 122 6.21 11.28 16 .22 .6 3.3 SHA 2.3 93 JAN 18 112 52.73 38 50.91 123 0.22 3.88 12 .10 .4 3.1 MAA 2.2 93 JAN 18 320 4.80 40 27.85 124 29.79 17.09 10 .06 2.5 .4 MEN 3.0 93 JAN 18 935 46.03 39 42.71 123 31.28 7.85 10 .08 .7 1.1 MAA 2.0 93 JAN 18 1629 59.24 36 10.50 118 1.93 2.03 11 .06 .8 2.5 OWV 3.1 93 JAN 18 1841 15.68 40 0.50 121 11.13 3.39 9 .06 .9 8.3 ALM - 2.1 93 JAN 18 1856 29.64 39 45.19 123 40.60 4.46 13 .11 .6 1.0 MAA 2.4 93 JAN 18 2327 10.66 38 50.47 122 46.40 3.09 42 .19 .3 .6 GEY 3.6 93 JAN 19 24 29.22 38 50.70 122 46.59 2.48 46 .19 .2 .8 GEY 3.5 93 JAN 19 32 41.85 38 49.83 122 47.64 2.51 9 .04 .3 .7 GEY 2.2 93 JAN 19 1309 2.32 40 22.43 122 5.24 6.24 7 .05 3.1 8.5 SHA - 2.2 93 JAN 19 1922 40.15 35 42.33 118 26.31 8.49 11 .09 .5 1.4 WWF 2.1 93 JAN 19 2123 43.75 38 49.82 122 47.39 2.24 11 .06 .3 .6 GEY 2.1 93 JAN 20 909 55.11 38 48.19 122 46.90 3.82 11 .18 .6 .7 GEY 2.2 93 JAN 20 1244 57.06 37 2.06 121 29.15 6.40 80 .12 .2 .5 CYS 2.4 93 JAN 20 1318 18.14 40 14.71 124 40.47 9.22 12 .1210.212.9 MEN - 3.2 93 JAN 21 251 36.10 40 2.94 122 8.61 3.30 7 .03 2.7 7.0 KLA - 2.2 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 ----------------------------------------------------------------------------- JAN 14 105333.3? 19.46 N 64.52 W 33N 4.4 0.9 16 VIRGIN ISLANDS 143044.6* 23.833N 143.389E 33N 4.8 1.2 39 VOLCANO ISLANDS REGION 170608.9? 36.66 N 98.31 W 5G 1.2 6 OKLAHOMA. mbLg 3.1 (TUL), 3.1 (GS). Felt at Cherokee, Helena, Jet and Nash. 223455.2* 18.617S 175.159W 158D 4.6 0.5 14 TONGA ISLANDS JAN 15 020250.5 35.038N 85.008W 5G 0.9 13 TENNESSEE. mbLg 3.1 (GS). Felt in the Chattanooga-Cleveland area and at Etowah. Also felt in northern Georgia. 110600.7 43.017N 144.201E 100G 5.9 0.9 191 HOKKAIDO, JAPAN REGION. Foreshock. 110606.3 43.040N 144.108E 100G 6.9 0.8 48 HOKKAIDO, JAPAN REGION. Mo=5.5*10**20 Nm (PPT). One person killed, at least 364 people injured and damage (VI JMA) at Kushiro, Hokkaido and Hachinohe, Honshu. Felt (V JMA) at Obihiro and Urakawa; (IV JMA) at Hakodate, Otaru and Tomakomai; (III JMA) at Sapporo, Hokkaido. Also felt (IV JMA) at Aomori and Morioka; (III JMA) at Akita, Fukushima, Sendai, Tokyo and Yokohama, 141757.4 39.215N 116.351W 10G 4.2 0.6 27 NEVADA JAN 16 062933.5 36.940N 121.581W 10G 4.8 0.8 33 CENTRAL CALIFORNIA. MD 5.1 (GM). area from Monterey to Santa Rosa. 105506.3* 20.688S 179.036W 600G 4.6 0.9 23 FIJI ISLANDS REGION JAN 17 053606.8* 19.612S 168.785E 33N 5.1 1.2 16 VANUATU ISLANDS 084748.0 42.150N 125.955W 10G 4.0 0.6 28 OFF COAST OF OREGON 102532.1 64.946N 149.403W 10G 4.3 0.8 19 CENTRAL ALASKA. ML 4.7 (AEIC). Felt at Fairbanks. 105123.6 43.586N 12.269E 10G 1.0 27 CENTRAL ITALY. ML 4.2 (VIE), 3.7 134936.1? 11.73 N 87.18 W 33N 4.9 1.1 42 NEAR COAST OF NICARAGUA JAN 18 011808.8 18.420N 145.887E 168D 5.8 0.8 69 MARIANA ISLANDS 093032.0 34.591N 116.578W 5G 0.5 14 SOUTHERN CALIFORNIA. ML 3.2 115532.0 34.597N 116.642W 5G 0.9 13 SOUTHERN CALIFORNIA. ML 3.3 124208.0 30.800N 90.220E 33N 5.7 5.7 0.8 48 XIJANG. Felt at Lhasa. 232710.2 38.829N 122.781W 5G 1.0 20 NORTHERN CALIFORNIA. ML 4.0 JAN 19 002429.2 38.831N 122.736W 5G 0.8 19 NORTHERN CALIFORNIA. ML 3.6 143927 Q 38.7 N 133.5 E 460 6.0 0.9 118 SEA OF JAPAN 230611 Q 1.2 N 126.1 E 33N 5.7 0.7 34 NORTHERN MOLUCCA SEA JAN 20 023056 Q 3.1 N 97.7 E 80 6.2 0.9 120 NORTHERN SUMATERA, INDONESIA 173115 Q 7.1 S 128.8 E 33N 6.3 0.8 41 BANDA SEA 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.