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 July 16 - 23, 1992 Data and text prepared by Steve Walter, Nan Macgregor-Scott, 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, July 22, 1992 the U.S. Geological Survey office in Menlo Park recorded 14 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 17 earthquakes recorded during the previous 7-day period, none of which were as large as M2.0. Most activity occurred early in the week, primarily in the southern part of the Bay Area on both the San Andreas and Calaveras faults. Last Thursday morning a M2.4 occurred on the southern Calaveras, about 1 mile southwest of Hollister (#1/1). That same afternoon another M2.4 occurred on the San Andreas about 5 miles east of Watsonville (#2/1). On Saturday evening small M2 earthquakes occurred on both the central Calaveras, about 12 miles north of Morgan Hill (#3/1), and on the San Andreas, about 3 miles west of San Juan Bautista (#4/1). Also on Saturday evening there was a M2.1 in the East Bay, about 12 miles north of Livermore (#5/1). This is the same location as a M3.4 event that occurred in July of last year and about two miles east of the M5.9 Livermore earthquake that occurred on January 24, 1980. Northern California The week began with a M4.0 earthquake about 12 miles north-northeast of Red Bluff last Thursday morning (#1/2). This event, which was felt from Redding to Sacramento, is the largest earthquake seen in this area in the 11 years that the USGS has maintained a seismic network in this part of the state. The focal depth of the earthquake was nearly 25 km, deep when compared to earthquakes in most other areas of the state, but not atypical of earthquakes in a zone that extends from Lake Shasta south to just west of Sutter Buttes. Earthquakes in this zone generally are deeper than normal, ranging from 10 to 30 km. Several other unusually deep earthquakes were recorded in the state in the two days following the Red Bluff earthquake. Just eighteen hours later a M2.5 event occurred 11 miles north of Redding (#2/2). Like the Red Bluff event, it occurred at a depth of 25 km. Ten hours later a 30km- deep, M2.8 event occurred beneath the central Sierra Nevada, about 38 miles northeast of Fresno (#4/2). This is nearly the same location, though slightly deeper, as a M2.2 event that occurred here in late January. The week's final deep earthquake occurred four hours later, a M2.8 event that was located 26 km beneath the San Joaquin Valley, about 33 miles southeast of Avenal (#5/2). Several areas continued to experience earthquake activity over three weeks after the activity was triggered by the M7.4 Landers earthquake in southern California. These areas include the Mono Lake basin (#7/2), the White Mountains area southeast of Mono Lake, and the Burney area north of Lassen Peak (#3/2). One area that began to experience seismicity only in the past week was the Carson Lake area, 20 miles east of Carson City, NV (#8/2). Several earthquakes larger than M3 shook the area on Monday, including a M4.1 event on Monday afternoon that was felt in the Fallon and Silver Springs areas. Aftershocks in the Cape Mendocino area continued to decay nearly three months after a M7.0 shook the area. During the past week only six aftershocks larger than M2 were recorded in the area (#9/2), the largest a M2.6 that occurred last Thursday night about 4 miles southwest of Eureka Just after midnight last Friday a M2.9 earthquake occurred about 20 miles east of Mount Shasta City (#6/2). It occurred at a shallow depth beneath the north side of Black Fox Mountain. This is the first earthquake to occur in this particular area since the USGS began monitoring seismicity in the region in 1981 and the largest earthquake in the Mount Shasta/Medicine Lake area in at least the past 18 months. Activity along the San Andreas system remained subdued. Only two M2 earthquakes were recorded south of the Bay Area, both on the creeping segment of the fault. North of the Bay Area, a M2.3 event occurred last Thursday along the Maacama fault west of Clear Lake. Just after noon on Wednesday a M2.2 event occurred on the Rogers Creek fault, about 2 miles northeast of Santa Rosa (#10/2). Long Valley Caldera Activity within the caldera continued to decline from the high levels that immediately followed the Landers earthquake. During the past week only five earthquakes occurred in the caldera, none as large as M2. All five were located in the south moat area, the main locus of activity since the caldera began to experience significant activity in 1980. A small cluster of earthquakes occurred in the Sierra Nevada terrane south of the caldera last Friday evening (#2/3). The largest of these, M3.8 event, was felt in Mammoth Lakes, just 11 miles to the north. The only other M2 earthquake in the area was a M2.1 event that occurred Monday evening in the Mount Morrison area (#3/3). USA Seismicity Aftershocks to the June 28 Landers earthquake continued to be felt in southern California during the week, though the rate of activity continues to decline. Only three aftershocks as large as M4 were recorded during the week, the largest a M4.5 event that occurred after noon Monday (#3/4). A number of earthquakes were recorded outside of California during the past week by the National Earthquake Information Center in Golden, CO. Most occurred in Nevada including a pair of M3.1 events in southeast Nye county east of Tonopah (#1/4), a cluster of M3-4 events near Carson Lake (#5/4-discussed above), and a M4.0 event northeast of Eureka (#6/4). Increased activity was also reported in the Yellowstone area of Wyoming. A M3.7 event just after midnight on Monday was felt in parts of Yellowstone National Park (#4/4). The Planet Earth A large earthquake occurred July 18 off the east coast of Honshu, Japan (#4/5). This Ms6.9 event was felt from Tokyo to the northeast coast of Hokkaido and produced a tsunami with wave heights of up to 46 cm along east coast of Honshu. The mainshock was preceded by M4.7 and M5.2 foreshocks and was followed by numerous aftershocks, including ten that were as large as M5. Several other earthquakes occurred along the margin of the northwest Pacific including a Mb5.9 event east of the Kuril Islands (#1/5) and a Mb5.0 event in eastern Siberia (#2/5). In the southwestern Pacific, a pair of M5 events occurred near the eastern coast of Papua New Guinea and a Ms5.6 earthquake occurred in the Tonga Islands region (#5/5). In the western hemisphere, a Mb5.7 earthquake occurred near the central coast of Peru (#3/5) and a Mb4.8 occurred in central Colombia. Finally, a Ms6.7 earthquake occurred north of the Arctic circle, along a mid-oceanic spreading ridge beneath the Greenland sea (#6/5). 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 JUL 16 1208 10.64 38 42.70 119 40.35 5.38 11 .09 7.2 3.6 WAK - 2.6 92 JUL 16 1341 51.78 36 50.04 121 24.62 9.22 76 .17 .3 .4 HOL 2.4 92 JUL 16 1342 59.59 39 9.57 123 9.63 5.31 16 .08 .4 1.3 MAA 2.3 92 JUL 16 1537 59.73 40 20.29 122 11.42 24.55 27 .27 .6 1.1 SHA 4.0 92 JUL 16 1714 35.06 38 47.82 122 48.47 3.76 26 .15 .3 .7 GEY 2.6 92 JUL 16 2106 50.33 36 16.47 120 50.35 7.04 32 .27 .6 1.2 BIT 2.0 92 JUL 16 2319 24.69 36 54.34 121 39.58 10.08 80 .18 .3 .5 SJB 2.4 92 JUL 16 2338 40.22 38 0.61 118 41.61 4.27 13 .23 2.8 5.8 MOL 2.0 92 JUL 17 250 46.88 40 14.32 124 20.58 3.96 8 .14 1.4 .6 MEN 2.5 92 JUL 17 505 47.53 40 44.60 124 12.89 9.53 16 .16 .7 .9 EUR 2.6 92 JUL 17 952 22.04 40 42.78 122 29.05 25.22 10 .26 1.2 2.3 SHA 2.5 92 JUL 17 1125 20.40 40 21.44 124 14.81 10.18 8 .06 .3 .9 MEN 2.1 92 JUL 17 1305 49.08 40 54.12 121 34.02 0.80 15 .18 .7 4.2 SHA * 2.3 92 JUL 17 1939 7.51 37 9.03 119 19.49 29.67 31 .10 .9 1.6 KAI 2.8 92 JUL 17 2337 57.56 35 41.46 119 40.66 26.29 33 .21 1.1 1.9 BAK 2.8 92 JUL 18 454 42.70 37 29.51 118 57.15 3.84 33 .09 .3 1.4 SIL 3.1 92 JUL 18 658 39.66 37 29.56 118 57.04 3.94 31 .12 .3 1.5 SIL 3.8 92 JUL 18 708 7.64 41 23.54 121 53.86 2.20 10 .15 .5 1.2 MOD 2.9 92 JUL 18 951 10.40 37 26.74 118 21.29 6.76 20 .10 .4 .9 CHV 2.2 92 JUL 18 2057 50.21 38 47.71 122 46.56 4.60 33 .17 .3 .6 GEY 2.1 92 JUL 19 51 24.04 40 24.12 124 42.83 11.55 7 .10 4.8 2.2 MEN 2.1 92 JUL 19 159 10.47 37 17.83 121 40.51 2.55 42 .09 .2 .6 SFL 2.1 92 JUL 19 316 59.91 36 51.11 121 35.24 6.78 50 .19 .3 .5 SJB 2.0 92 JUL 19 657 24.10 37 50.70 121 45.84 14.66 34 .15 .5 .6 GRN 2.1 92 JUL 19 822 56.31 36 36.34 121 12.78 8.91 49 .12 .2 .4 PIN 2.2 92 JUL 19 855 1.71 37 29.67 118 56.98 0.42 19 .10 .6 8.9 SIL - 2.0 92 JUL 19 1124 58.57 38 48.75 122 50.12 0.02 17 .12 .3 1.7 GEY * 2.0 92 JUL 19 1512 55.61 37 56.11 118 34.84 7.04 24 .14 1.6 3.5 MOL 2.2 92 JUL 20 108 12.47 37 38.46 118 6.73 0.10 16 .11 3.5 4.8 WHI * 2.1 92 JUL 20 109 21.48 37 39.55 118 2.74 1.36 20 .16 3.311.8 WHI - 2.3 92 JUL 20 1519 5.61 39 9.58 119 25.46 5.01 9 .1410.0 9.1 WAK - 2.4 92 JUL 20 1722 26.38 39 13.06 119 29.55 3.98 13 .2611.2 8.1 WAK * 3.1 92 JUL 20 1736 8.11 39 17.22 119 18.42 5.04 39 .33 2.524.2 NEV - 3.4 92 JUL 20 1906 58.53 39 17.40 119 18.76 0.16 38 .37 2.3 8.0 NEV * 3.7 92 JUL 20 1915 53.06 39 12.60 119 29.39 3.14 13 .2310.6 9.9 WAK * 3.0 92 JUL 20 2009 33.63 39 15.83 119 21.23 1.16 45 .24 1.2 5.4 WAK 4.1 92 JUL 21 150 7.72 39 13.82 119 33.00 2.53 14 .3711.411.8 WAK * 3.1 92 JUL 21 446 23.32 37 32.91 118 51.67 10.99 34 .13 .4 1.0 MOR 2.1 92 JUL 21 1158 24.71 39 13.23 119 23.45 1.25 16 .19 2.1 7.4 WAK * 3.1 92 JUL 21 1301 48.60 39 11.77 119 29.02 3.85 16 .20 9.9 7.3 WAK * 2.9 92 JUL 21 1344 6.70 38 48.52 122 46.47 1.50 23 .16 .3 1.3 GEY 2.1 92 JUL 22 54 1.19 40 20.49 124 29.79 15.02 8 .20 3.2 1.1 MEN 2.5 92 JUL 22 1013 5.21 38 3.29 118 51.51 6.38 26 .13 1.913.0 MOL - 2.4 92 JUL 22 1935 4.30 38 27.72 122 41.08 7.75 34 .17 .3 .9 ROG 2.2 92 JUL 23 629 3.73 40 17.84 124 22.93 8.58 9 .06 1.1 .7 MEN 2.3 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 ------------------------------------------------------------------------------ JUL 16 151129.9& 61.670N 150.910W 53 63 SOUTHERN ALASKA. . ML 2.8 153800.0& 40.337N 122.197W 17 14 NORTHERN CALIFORNIA. . MD 4.0 (GM). ML 3.9 (BRK). Felt in the Redding-Chico-Sacramento area. 183303.1 38.323N 116.159W 5G 0.7 12 NEVADA. ML 3.1 (GS). 215820.0 34.925N 116.915W 5G 0.5 15 SOUTHERN CALIFORNIA. MD 3.5 JUL 17 041136.2 44.381N 150.392E 33N 5.9 5.1 0.9 50 EAST OF KURIL ISLANDS 060012.5 38.387N 116.120W 5G 0.8 11 NEVADA. ML 3.1 (GS). 110301.7* 60.807N 166.997E 33N 5.0 4.8 1.0 60 EASTERN SIBERIA, RUSSIA 184558.9* 10.470S 78.298W 46D 5.7 5.1 0.7 64 NEAR COAST OF PERU. Mo=1.6*10**18 Nm (PPT). Felt at Barranca, Chimbote, Huacho and Huaraz. Felt (III) at Lima. JUL 18 014053.7? 4.44 N 75.28 W 150G 4.8 0.8 35 COLOMBIA. Felt in Antioquia, Caldas, Quindio and Risaralda Departments. 075746.5* 6.446S 147.900E 33N 5.1 5.1 1.1 13 EASTERN NEW GUINEA REG., P.N.G. 081517.2 39.511N 143.167E 33N 4.7 1.0 35 OFF EAST COAST OF HONSHU, JAPAN 082001.8 39.432N 143.234E 33N 5.2 0.9 66 OFF EAST COAST OF HONSHU, JAPAN 083659.2 39.408N 143.353E 33N 5.9 6.9 0.9 118 OFF EAST COAST OF HONSHU, JAPAN. Mo=2.5*10**19 Nm (PPT). Felt (III JMA) at Aomori, Hachinohe, Ishinomaki, Miyako, Sakata and Sendai; (II JMA) at Akita and Fukushima; (I JMA) at Kofu, Tokyo, Tateyama and Utsunomiya, Honshu. Also felt (II JMA) at Kushiro, Nemuro and Obihiro, Hokkaido. Tsunami generated with maximum wave heights (peak-to-trough) of 46 cm. at Ofunato, 42 cm. at Miyako, 28 cm. at Aikawa and 24 cm. at Hachinohe. 083906.0* 39.724N 143.019E 33N 5.8 1.1 45 OFF EAST COAST OF HONSHU, JAPAN 094505.1? 39.77 N 143.00 E 33N 4.6 0.8 16 OFF EAST COAST OF HONSHU, JAPAN 102013.1 39.526N 143.011E 33N 5.8 6.1 1.0 96 OFF EAST COAST OF HONSHU, JAPAN. 105940.3 39.404N 143.206E 33N 5.1 1.0 75 OFF EAST COAST OF HONSHU, JAPAN 110652.0? 39.33 N 143.37 E 33N 4.6 0.7 13 OFF EAST COAST OF HONSHU, JAPAN 111013.2? 39.50 N 143.49 E 33N 4.8 0.8 25 OFF EAST COAST OF HONSHU, JAPAN 111113.0? 39.81 N 143.28 E 33N 5.0 1.2 22 OFF EAST COAST OF HONSHU, JAPAN 114614.2* 39.353N 143.467E 33N 4.6 0.5 14 OFF EAST COAST OF HONSHU, JAPAN 114818.4 39.248N 143.164E 13D 5.3 0.8 63 OFF EAST COAST OF HONSHU, JAPAN 120241.7 39.148N 143.174E 33N 5.2 0.8 67 OFF EAST COAST OF HONSHU, JAPAN 135655.2 39.455N 142.996E 33N 5.4 5.3 0.8 66 NEAR EAST COAST OF HONSHU, 144546.7 39.344N 143.261E 33N 4.7 0.8 44 OFF EAST COAST OF HONSHU, JAPAN 153143.2* 22.600S 175.136W 33N 5.1 5.6 0.9 40 TONGA ISLANDS REGION 172712.1 39.716N 143.117E 33N 4.8 5.4 0.8 46 OFF EAST COAST OF HONSHU, JAPAN 181213.3 39.111N 143.156E 33N 5.1 4.9 0.8 55 OFF EAST COAST OF HONSHU, JAPAN 205513.2* 39.545N 143.258E 33N 5.2 5.2 1.0 57 OFF EAST COAST OF HONSHU, JAPAN 211856.7 39.277N 142.959E 33N 5.2 5.6 1.3 77 NEAR EAST COAST OF HONSHU, 213624.8* 30.795N 137.306E 475D 4.9 0.8 51 SOUTH OF HONSHU, JAPAN JUL 19 003239.5 37.179N 117.241W 5G 0.7 15 CALIFORNIA-NEVADA BORDER REGION. ML 3.2 (GS). 024008.6* 6.558S 147.680E 33N 4.9 1.2 22 EASTERN NEW GUINEA REG., P.N.G. JUL 20 044800.2 34.935N 116.938W 5G 4.3 0.9 28 SOUTHERN CALIFORNIA. MD 4.4 070329.1* 44.802N 110.367W 5G 0.9 10 YELLOWSTONE REGION, WYOMING. ML 3.7 (GS). Felt in parts of Yellowstone National Park. 074649.0* 78.776N 3.938E 10G 5.5 6.7 1.2 44 GREENLAND SEA 131319.0 34.986N 117.006W 5G 4.4 0.9 26 SOUTHERN CALIFORNIA. MD 4.5 190657.1 39.400N 119.087W 5G 1.2 17 NEVADA. ML 3.8 (GS). Felt at Fernley and Silver Springs. 200931.2 39.335N 119.107W 5G 4.1 0.8 21 NEVADA. Felt in the Fallon Fernley-Silver Springs area JUL 21 205805 Q 39.4 N 115.6 W 5G 0.8 22 NEVADA. ML 4.0 (GS). 232209 Q 34.1 N 116.6 W 5G 0.6 18 SOUTHERN CALIFORNIA. ML 4.0 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.