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 May 14 - 20, 1992 data and text prepared by Steve Walter, Nan Macgregor-Scott, Barry Hirshorn, Allan Lindh U.S. Geological Survey 345 Middlefield Rd. MS-977, Menlo Park, CA 94025 Graphics by Quentin Lindh San Francisco Bay Area The number of earthquakes in the Bay Area in the past seven days remained about the same as during the previous week, although the number of M2 earthquakes declined. For the 7-day period ending at midnight on Wednesday, May 20, 1992 the U.S. Geological Survey office in Menlo Park recorded 21 earthquakes of magnitude one (M1) and greater within the San Francisco Bay area shown in Figure 1. Only one of these was as large as M2.0. This compares with 23 earthquakes recorded during the previous 7-day period, five of which were as large as M2.0. The lone M2 earthquake occurred last Thursday afternoon along the southern Calaveras fault about 6 miles northeast of Gilroy (#1 in Fig.1). A M3.1 event occurred in nearly the same location during January of this year and numerous M2 events have occurred here during the past 18 months. Seven M1 earthquakes occurred along the creeping segment of the San Andreas in the vicinity of San Juan Bautista. Several other small events occurred in the Santa Cruz Mountain segment that ruptured in the Loma Prieta earthquake including one event along the Zayante fault that parallels the San Andreas northwest of Watsonville. There was only minor activity in the East Bay: a M1 event at the south end of the Concord fault, about 9 miles southeast of Concord, and a M1.4 on the Hayward fault, about 4 miles east of downtown Oakland. Northern California Aftershocks to the M7.0 April 25th Cape Mendocino earthquake continue to dominate the map of seismicity for northern California (Figure 2). During the past week there were nine aftershock as large as M3, including the week's largest earthquake, a M4.0 event late Monday night (#2/2). Most of these larger aftershocks were located along the Mendocino escarpment west of Punta Gorda. Other earthquakes of note in the north state include a pair of M2 events beneath the central Klamath Mountains, about 40 miles east of Eureka (#5/2), and a M2.7 event near Lake Almanor, about 15 miles southeast of Lassen Peak (#4/2). In eastern California there was one aftershock (#1/2) to the active sequence east of Markleeville that was described in last week's report. On Friday evening a M2.7 event occurred in the central Sierra Nevada just west of Ebbetts Pass (#3/2) and on Sunday afternoon a M2.4 event occurred about 20 miles southeast of Yosemite Valley (#7/2). In central California the only notable activity occurred on the southern end of the creeping segment of the San Andreas where a M3.0 event occurred early Saturday about 17 miles northeast of San Ardo (#6/2). Long Valley Caldera Two M2 earthquakes occurred in the central caldera beneath the resurgent dome area, the largest a M2.9 event last Friday afternoon (#2/3). During the past 12 years that Long Valley has been closely monitored the resurgent dome has proved much less active than the south moat area, experiencing mostly scattered, small events . The most recent activity here was a small cluster of M2 events in September of last year. One other M2 earthquake occurred just inside the southern rim of the caldera (#3/3), with three small earthquakes at the west end of the south moat area, near the town of Mammoth Lakes. USA Seismicity Earthquakes also occurred in states other than California, according to information obtained by the National Earthquake Information Center. The largest of these was a M3.7 event that occurred early Tuesday morning in eastern Idaho, about 20 miles north-northwest of Borah Peak (#2/4). By coincidence, a small earthquake occurred just minutes later on the opposite side of the country. This M2.0 event was located in western Virginia along the border with North Carolina (#3/4). Though quite small, it was reported to have been felt at Hillsville, VA. The only other notable earthquake in the lower 48, outside of California, was a M2.8 event in southwestern Colorado that was felt in Montrose and Olathe (#1/4). The Planet Earth A number of moderate to large earthquakes occurred worldwide during the past week according to data from the USGS National Earthquake Information Center. The largest of these was a Ms7.3 event on Sunday off the southeast coast of the Philippines (#3/5). This large earthquake was preceded about 25 minutes earlier by a M5.8 foreshock. A second M7 earthquake occurred in the southwest Pacific earlier in the week near the northeast coast of Papua New Guinea (#1/5). Several moderate earthquakes occurred in the Himalayan Range starting with a Mb5.9 event last Friday in Kyrgyzstan (#2/5). It was widely felt in Kyrgyzstan, Uzbekistan, and Kazakhstan. On Wednesday, a slightly larger Ms6.2 earthquake occurred several hundred miles to the south in northern Pakistan (#5/5). Later the same day, a Mb6.1 earthquake occurred in northern Xinjiang province in northwestern China (#6/5). Several moderate earthquakes occurred along the Pacific coasts of Central and South America, the largest a Ms5.9 event just south of Panama (#4/5). Table 1. Central California Seismicity (M>2.0) (only Mendocino events > M3.0 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 MAY 14 2100 15.81 38 41.25 119 38.82 0.04 17 .17 1.4 1.5 WAK * 2.6 92 MAY 14 2259 19.16 37 3.01 121 29.44 5.73 80 .15 .2 .5 CYS 2.2 92 MAY 14 2333 16.02 40 27.49 124 21.12 0.05 20 .16 .8 1.5 MEN * 3.2 92 MAY 15 634 38.91 36 33.56 121 1.88 7.08 35 .19 .4 .9 PAN 2.0 92 MAY 15 1038 14.94 40 17.01 124 21.74 7.45 24 .16 .7 .3 MEN 3.4 92 MAY 15 1111 33.02 38 47.45 122 45.42 0.90 38 .17 .3 .8 GEY 2.5 92 MAY 15 2302 27.32 40 16.64 121 7.01 5.32 25 .15 .9 1.8 ALM 2.9 92 MAY 16 139 50.62 37 40.24 118 51.50 3.74 35 .16 .3 .7 DOM 2.9 92 MAY 16 402 6.85 38 26.86 119 54.73 1.25 9 .1612.6 8.9 YOS - 2.7 92 MAY 16 543 6.07 40 52.91 123 27.15 21.19 9 .12 .5 .9 KLA 2.0 92 MAY 16 1245 31.43 36 14.54 120 48.46 6.30 71 .25 .3 .7 BIT 3.0 92 MAY 16 2039 49.90 36 11.21 120 14.77 8.69 12 .15 .4 1.0 COA 2.0 92 MAY 16 2106 5.96 37 40.23 118 51.10 1.91 17 .12 .3 .7 DOM 2.0 92 MAY 17 1612 35.65 37 37.39 118 54.97 5.86 31 .17 .4 .6 SMO 2.3 92 MAY 17 2150 36.51 40 28.55 124 20.89 15.07 18 .10 .7 .3 MEN 3.1 92 MAY 17 2151 26.74 40 28.37 124 21.31 16.04 12 .06 .8 .4 MEN 3.2 92 MAY 17 2325 50.48 37 29.44 119 22.59 14.02 16 .09 .5 1.7 KAI 2.4 92 MAY 18 417 57.55 36 23.83 120 44.63 14.22 18 .15 .5 .8 CRV 2.0 92 MAY 18 431 3.65 36 24.08 120 45.48 13.60 24 .17 .5 .7 CRV 2.0 92 MAY 18 710 53.02 40 18.30 124 46.65 10.49 9 .19 5.2 2.8 MEN 3.1 92 MAY 18 728 28.20 36 23.93 120 45.53 13.79 30 .17 .4 .7 CRV 2.2 92 MAY 18 742 31.72 40 19.09 124 42.29 11.83 16 .21 4.9 2.1 MEN 4.0 92 MAY 18 752 16.65 40 17.84 124 25.49 8.70 19 .12 .9 .4 MEN 3.4 92 MAY 18 1029 25.33 40 23.45 124 15.67 10.77 22 .14 .4 .3 MEN 3.0 92 MAY 18 1947 44.69 37 24.54 118 32.39 5.25 21 .09 .2 .8 CHA 2.1 92 MAY 19 237 45.17 38 49.41 122 46.66 0.04 47 .32 .5 .6 BP 2.1 92 MAY 20 230 48.44 40 16.02 124 34.52 2.15 38 .21 1.9 4.3 CP 3.7 92 MAY 20 454 0.68 36 22.17 120 58.69 2.75 50 .35 .7 .8 CR 2.1 92 MAY 20 1820 58.60 38 48.95 122 48.90 0.29 59 .44 .7 .7 BP 2.2 92 MAY 21 27 37.03 38 49.88 122 48.18 0.03 39 .49 .8 .8 BP 2.0 92 MAY 21 338 0.12 40 17.92 124 32.11 19.36 42 .28 2.1 .9 CR 3.5 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 ----------------------------------------------------------------------------- -- MAY 14 150054.6 35.172N 2.413W 10G 3.5 1.1 24 STRAIT OF GIBRALTAR. mbLg 3.9 154812.2 35.269N 2.455W 25 3.6 1.0 20 STRAIT OF GIBRALTAR. mbLg 3.7 172817.6 21.077S 179.325W 600G 4.9 0.8 57 FIJI ISLANDS REGION 232832.2 45.688N 151.435E 33N 4.8 4.3 0.8 38 KURIL ISLANDS MAY 15 051529.2* 33.901N 116.278W 10G 1.1 6 SOUTHERN CALIFORNIA. ML 2.7 052226.6* 52.017N 160.252E 41D 4.7 4.5 0.9 26 OFF EAST COAST OF KAMCHATKA 053136.2* 54.996N 161.636E 50D 4.7 4.2 0.9 28 NEAR EAST COAST OF KAMCHATKA 060221.1 60.322N 152.581W 130 0.7 58 SOUTHERN ALASKA 070503.0 6.021S 147.563E 33N 6.3 7.0 1.0 71 EASTERN NEW GUINEA REG., P.N.G. 080759.6* 40.733N 72.590E 33N 5.9 1.1 70 KYRGYZSTAN. 083508.3? 16.91 N 99.80 W 26D 4.0 1.1 19 NEAR COAST OF GUERRERO, MEXICO. 092402.8 33.962N 116.251W 10G 0.4 9 SOUTHERN CALIFORNIA. ML 2.9 213208.8? 16.12 N 98.43 W 33N 5.1 3.8 1.1 33 NEAR COAST OF GUERRERO, MEXICO. 213624.3 38.563N 107.914W 5G 1.0 8 COLORADO. ML 2.8 (GS). 214917.2* 18.375N 147.330E 13D 5.0 4.9 1.2 30 MARIANA ISLANDS REGION 220623.3 52.425N 172.169W 33N 5.0 4.6 0.8 61 ANDREANOF ISLANDS, ALEUTIAN IS. MAY 16 013950.3 37.660N 118.869W 5G 0.6 10 CALIFORNIA-NEVADA BORDER REGION. 023835.9? 31.87 S 177.79 W 33N 5.3 5.6 0.8 14 KERMADEC ISLANDS REGION 102148.8* 52.745N 174.812E 150D 4.6 1.0 33 NEAR ISLANDS, ALEUTIAN ISLANDS 145821.3? 19.18 S 168.48 E 33N 5.6 4.9 0.7 55 VANUATU ISLANDS 205758.0? 13.65 S 75.68 W 57D 5.4 0.7 40 CENTRAL PERU. Felt at Ica, Lima MAY 17 062129.8 33.946N 116.280W 10G 0.6 9 SOUTHERN CALIFORNIA. ML 3.2 094924.5? 8.36 N 127.02 E 33N 6.0 6.8 1.0 36 PHILIPPINE ISLANDS REGION 101536.2? 7.93 N 127.32 E 33N 5.8 7.3 0.8 33 PHILIPPINE ISLANDS REGION 153621.6 6.990N 126.677E 46D 5.1 5.2 1.1 39 MINDANAO, PHILIPPINE ISLANDS 204246.2? 21.25 S 68.82 W 105D 5.2 0.6 37 CHILE-BOLIVIA BORDER REGION 213600.1* 6.127S 152.899E 33N 5.7 5.5 1.1 28 NEW BRITAIN REGION, P.N.G. MAY 18 002233.0 33.896N 116.297W 10G 0.7 9 SOUTHERN CALIFORNIA. ML 3.3 030221.8? 33.47 S 71.45 W 33N 5.5 5.6 0.8 34 NEAR COAST OF CENTRAL CHILE 032544.3? 7.44 N 126.60 E 33N 5.2 0.6 14 MINDANAO, PHILIPPINE ISLANDS 110243.7 20.116S 177.859W 538D 5.0 0.6 59 FIJI ISLANDS REGION 154416.2 33.875N 116.282W 10G 4.8 1.1 37 SOUTHERN CALIFORNIA. MD 4.8 231923.6* 7.942N 82.793W 10G 5.8 5.9 1.3 72 SOUTH OF PANAMA MAY 19 081722.6& 44.499N 113.988W 5G 20 EASTERN IDAHO. . ML 3.7 084506.3& 36.767N 80.710W 5G 12 VIRGINIA. . MD 2.0 122456.9* 28.158N 55.426E 33N 5.7 5.1 0.6 26 SOUTHERN IRAN 144255.5? 8.30 S 159.47 E 33N 5.6 5.4 0.5 41 SOLOMON ISLANDS. Mo=7.9*10**17 MAY 20 122035 Q 33.6 N 71.3 E 33N 6.2 0.9 70 PAKISTAN MAY 21 050005 Q 42.1 N 89.0 E 33N 6.1 0.9 73 NORTHERN XINJIANG, CHINA