- Earthquake summary

MODERATELY LARGE QUAKE SHAKES ICELAND

EARTHQUAKE SUMMARY FOR OCTOBER 20, 2020

An M 5.6 earthquake in Iceland today was accompanied by a series of lighter shocks. The mainshock was reported felt in southwestern Iceland with intensity V in Keflavik and IV in Harnarfjordur, Gardabaei, Alflanes, Kopavogur, Seltjarnarnes, Reykajik, Grundarhverfi and III in Mosfellsbaer, and Vogar. This earthquake occurred within minutes of local solar noon and was likely promoted by high tidal stresses of the new moon which maximize near this time. This is the strongest earthquake in southern Iceland within about 200 km of this epicenter since an M 6.3 more than 12 years ago on May 29, 2008. Other such events occurred in 1998 and 2000. It is likely that this was triggered by energy from the Alaska Peninsula quake of M 7.5 yesterday combined with high tidal stresses and by the geomagnetic storm of the past day. Forecast 128029 had expected today's event was likely in southern Iceland around October 17. Iceland is located at the sixth node (60 degrees) from the activity in the Alaska Peninsula. An earthquake of M 5.3 in the northern Mariana Islands today was also at this distance from the Alaska Peninsula. It is also at 100 degrees from the M 6.8 in Atacama, Chile of September 1, 2020 and may have been promoted by energy from that source.

O: 20OCT2020 13:51:36 63.9N 22.3W ML=3.2 EMSC ICELAND REGION

O: 20OCT2020 14:01:43 63.9N 22.1W ML=3.6 EMSC ICELAND REGION

O: 20OCT2020 14:04:48 63.9N 22.1W ML=3.1 EMSC ICELAND REGION

O: 20OCT2020 14:28:14 63.9N 22.2W ML=3.0 EMSC ICELAND REGION

O: 20OCT2020 14:30:38 63.9N 22.2W ML=3.1 EMSC ICELAND REGION

O: 20OCT2020 14:35:50 63.9N 22.2W ML=3.7 EMSC ICELAND REGION

O: 20OCT2020 14:40:04 63.9N 22.0W ML=3.0 EMSC ICELAND REGION

O: 20OCT2020 14:45:35 63.9N 22.2W ML=3.1 EMSC ICELAND REGION

O: 20OCT2020 15:17:19 63.9N 22.0W ML=3.1 EMSC ICELAND REGION

O: 20OCT2020 15:22:54 63.9N 22.2W ML=3.0 EMSC ICELAND REGION

O: 20OCT2020 15:27:12 63.9N 22.3W ML=3.8 EMSC ICELAND REGION

O: 20OCT2020 15:28:16 63.9N 22.3W ML=3.6 EMSC ICELAND REGION

O: 20OCT2020 15:30:36 63.9N 22.3W ML=3.0 EMSC ICELAND REGION

O: 20OCT2020 15:32:45 63.9N 22.3W ML=4.0 EMSC ICELAND REGION

O: 20OCT2020 15:33:47 63.9N 22.2W ML=3.6 EMSC ICELAND REGION

O: 20OCT2020 15:35:24 63.9N 22.2W ML=3.1 EMSC ICELAND REGION

O: 20OCT2020 18:47:18 63.9N 22.0W ML=3.1 EMSC ICELAND REGION

O: 21OCT2020 00:22:39 63.9N 22.0W ML=3.3 EMSC ICELAND REGION

O: 21OCT2020 02:22:47 63.9N 22.1W ML=3.0 EMSC ICELAND REGION

O: 21OCT2020 06:05:15 63.9N 22.3W ML=3.4 EMSC ICELAND REGION

O: 21OCT2020 06:23:19 63.9N 22.3W ML=3.4 EMSC ICELAND REGION

O: 20OCT2020 13:43:16 64.0N 22.1W Mw=5.5 EMSC ICELAND REGION

O: 20OCT2020 17:22:45 64.0N 22.1W ML=3.0 EMSC ICELAND REGION

O: 20OCT2020 14:20:34 64.8N 23.8W ML=3.1 EMSC ICELAND REGION

O: 20OCT2020 13:49:22 63.9N 22.1W ML=3.0 EMSC ICELAND REGION

O: 20OCT2020 15:07:45 64.8N 21.3W ML=3.1 EMSC ICELAND

P: 17OCT2020 128029 63.0N 26.0W 3.0-4.4 ABBAA Iceland area

Other moderate earthquakes at high latitudes today, apparently related to the

M 7.5 in Alaska occurred as aftershocks in Alaska and in the Queen Charlotte Island area of British Columbia (M 4.6) and in the South Shetland Islands (M 5.0). The largest earthquakes in the U.S. or Canada today were aftershocks south of Alaska. These included an M 5.0 felt with light intensity in the Chugiak, Alaska area.

An earthquake of M 4.8 in the Unimak Island region about 300 km west of the epicenter of the M 7.5 in the Alaska Peninsula occurred today. This is the strongest earthquake in the Unimak area since an M 5.6 on August 13, the only such event in the past year in the Unimak area. A minor swarm occurred on July 29 and 30 in the area at the end of July, 2020. Today's event was probably a regional aftershock of the M 7.5 in the Alaska Peninsula yesterday. Forecast 12022 had expected today's activity in the Unimak Island area was likely around October 18-22.

NEIC reported this earthquake of M 4.8 in the Unimak Islands was felt with intensity IV in the area(s) of the Unimak Islands at Unalaska, Alaska.

O: 21OCT2020 03:35:25 53.1N 164.6W Mw=4.8 EMSC UNIMAK ISLAND REGION, ALASKA

P: 18OCT2020 128022 54.2N 165.0W 3.5-4.8 BAAAA Unimak Islands, Aleutians

P: 22OCT2020 128022 54.5N 163.5W 3.5-4.8 ABAAA Unimak Islands, Aleutians

A listing of events in the Alaska aftershock zone of M>=4.0 follows. A more complete list can be found in the "ALASKA" regional section of this report.

O: 20OCT2020 08:06:44 54.2N 159.8W mb=4.4 EMSC SOUTH OF ALASKA

O: 20OCT2020 13:36:02 54.3N 159.6W mb=4.0 EMSC SOUTH OF ALASKA

O: 20OCT2020 07:37:00 54.4N 159.8W mb=4.7 EMSC SOUTH OF ALASKA

O: 20OCT2020 08:16:36 54.4N 159.7W mb=4.0 EMSC SOUTH OF ALASKA

O: 20OCT2020 12:32:12 54.4N 159.8W Mw=5.2 EMSC SOUTH OF ALASKA

O: 21OCT2020 01:17:54 54.4N 159.6W Mw=5.1 EMSC SOUTH OF ALASKA

O: 21OCT2020 06:37:35 54.4N 159.7W mb=4.9 EMSC SOUTH OF ALASKA

O: 20OCT2020 22:42:35 54.5N 159.9W mb=4.2 EMSC SOUTH OF ALASKA

O: 20OCT2020 08:18:42 54.6N 159.7W mb=4.8 EMSC SOUTH OF ALASKA

O: 20OCT2020 21:38:53 54.6N 159.7W mb=4.9 EMSC SOUTH OF ALASKA

O: 21OCT2020 00:33:51 54.6N 159.7W mb=4.0 EMSC SOUTH OF ALASKA

O: 20OCT2020 08:37:13 54.7N 159.8W mb=5.0 EMSC SOUTH OF ALASKA

O: 20OCT2020 23:57:58 54.7N 159.7W mb=4.0 EMSC SOUTH OF ALASKA

P: 17OCT2020 128007 54.8N 158.7W 3.5-4.8 BAAAA Alaska Peninsula

The M 4.6 in the Queen Charlotte Islands area which followed the M 7.5 in the Alaska Peninsula yesterday appears to have been a real, triggered event. ECAN reported a number of associated quakes which suggest the event of M 4.6 was real. This is an excellent example of a true P- or S- phase triggered event. In the previous issue of this report it had been noted as:

"An earthquake in Queen Charlotte Island, Canada of M 4.6 was reported by Earthquakes Canada four minutes after the Alaska Peninsula M 7.5. It may be a ghost event created by misreading of an automatic earthquake algorithm or a real event triggered by energy from Alaska." (October 19-20, 2020)

The last earthquake of M 4.6 or greater within about 200 km of this epicenter occurred six years ago on September 27, 2014. Forecast 128010 had expected this activity was likely within about 100 km of this epicenter around October 14. This epicenter is at 16 degrees from the Alaska Peninsula event and the quake occurred as the P-wave from that epicenter passed through the region.

O: 19OCT2020 20:58:07 52.0N 133.3W MB=4.6 ECAN OF VILLAGE OF QUEEN CHARLOTTE,

P: 14OCT2020 128010 52.0N 132.0W 3.0-4.9 BAAAA British Colombia

The strongest earthquake in the world today was an M 5.9 in the Tonga Islands. It occurred near local solar noon and was probably promoted by high tidal stresses which maximize near this hour. This epicenter is near the fifth node from the Alaska Peninsula (72 degrees) and was probably promoted by energy from that source. An M 6.4 occurred about 200 km southwest of this epicenter on October 1, 2020 but the last event of equal or greater magnitude within this area was an M 6.2 on November 2, 2013. Forecast 128056 had expected today's event within about 50 km of today's epicenter was likely around October 16.

O: 21OCT2020 00:22:34 19.3S 172.4W Mw=5.9 EMSC TONGA REGION

O: 20OCT2020 18:57:54 19.4S 174.1W mb=5.0 EMSC TONGA

P: 16OCT2020 128056 19.0S 173.0W 4.0-5.3 BAAAA Tonga Islands

OTHER GLOBAL EARTHQUAKE ACTIVITY

For most events there are two listings. The first line is the observed event starting with "O:" for Observed. There follows the date, month and year, the time in UT hours:minutes:seconds, the latitude and longitude, the given magnitude and the reporting agency followed by the geographic location. The second line starts with "P:" This is the forecast event as forecast in our summaries normally more than a month in advance. Magnitudes may vary in response to updated seismic watches and daily variations due to tidal and other influences. This line has the forecast date, month and year, the forecast number, latitude, longitude and forecast magnitude range. This is followed by a comparison between the forecast and the event. The comparison includes letters A-D. The first is number of days difference from predicted (A:up to 2, B3-5; C:6-10; D:more than 10), Difference in latitude (A:up to 1 degree; B:1-2 degrees; C:2-4 degrees; D:more than 4 degrees); longitude (same comparison as with latitude); magnitude (A: within forecast range; B: higher than forecast range; C: lower than forecast range; D: no comparison possible). The last letter is a stand in for a future comparison which needs to be done statistically after a large number of forecasts have been made. In previous data, an excellent match is generally AAAAA; a good match as one or two B's; a fair match has several B's and C's and a poor match is one which contains a number of C's or D's.

ASIA

O: 20OCT2020 19:55:42 27.4N 96.6E ML=4.2 EMSC MYANMAR-INDIA BORDER REGION

P: 21OCT2020 127952 32.0N 95.0E 3.5-4.8 ACBAA So. China

O: 21OCT2020 04:04:51 32.0N 104.3E mb=5.1 EMSC EASTERN SICHUAN, CHINA

P: 11OCT2020 127660 28.0N 104.0E 4.0-5.3 CCAAA Myanmar

O: 20OCT2020 22:30:29 38.3N 75.4E mb=4.3 EMSC SOUTHERN XINJIANG, CHINA

P: 18OCT2020 127929 38.0N 74.0E 3.8-5.1 AAAAA Hindu Kush/Pakistan

O: 20OCT2020 22:58:48 36.5N 70.2E mb=4.2 EMSC HINDU KUSH REGION, AFGHANISTAN

P: 22OCT2020 127929 36.0N 72.0E 3.8-5.1 AABAA Hindu Kush/Pakistan

O: 20OCT2020 23:08:06 41.3N 73.1E mb=4.7 EMSC KYRGYZSTAN

P: 22OCT2020 127974 40.0N 75.0E 4.0-5.3 ABBAA Kirgizstan/Xinjiang

INDONESIA AND PHILIPPINES

O: 20OCT2020 13:46:59 1.2S 99.4E ML=4.5 EMSC P. MENTAWAI REGION, INDONESIA

P: 21OCT2020 127869 2.0S 99.0E 4.0-5.3 AAAAA So. of Sumatera

O: 21OCT2020 00:30:33 1.3S 120.0E ML=4.4 EMSC SULAWESI, INDONESIA

P: 15OCT2020 127838 0.0N 120.0E 4.0-5.3 CBAAA Celebes Sea

O: 20OCT2020 09:27:02 1.7N 127.1E ML=4.4 EMSC HALMAHERA, INDONESIA

P: 20OCT2020 127855 1.0S 127.0E 4.0-5.3 ACAAA Ceram area

O: 21OCT2020 04:21:22 2.8N 96.2E mb=4.6 EMSC SIMEULUE, INDONESIA

P: 16OCT2020 127850 3.0N 99.0E 4.0-5.3 BABAA So. Sumatera

O: 21OCT2020 00:40:14 3.9S 136.0E mb=4.4 EMSC PAPUA, INDONESIA

P: 17OCT2020 127872 1.0S 137.0E 4.0-5.3 BCAAA West Irian, PNG

O: 20OCT2020 15:28:21 4.9S 133.8E ML=4.1 EMSC NEAR S COAST OF PAPUA, INDONESI

P: 14OCT2020 127872 4.0S 134.0E 4.0-5.4 CAAAA West Irian, PNG

O: 20OCT2020 17:28:10 5.1S 141.1E ML=4.0 EMSC NEW GUINEA, PAPUA NEW GUINEA

P: 21OCT2020 127872 5.0S 139.0E 4.0-5.4 AABAA West Irian, PNG

O: 20OCT2020 23:40:40 7.4S 129.2E ML=4.1 EMSC KEPULAUAN BABAR, INDONESIA

P: 18OCT2020 127873 6.0S 130.0E 4.0-5.3 ABAAA West Irian, PNG

O: 21OCT2020 03:44:36 8.7S 116.1E ML=4.1 EMSC LOMBOK REGION, INDONESIA

P: 18OCT2020 128054 11.0S 115.0E 4.0-5.3 BCAAA So. of Indonesia

O: 20OCT2020 13:20:02 18.0N 146.2E Mw=5.3 EMSC ALAMAGAN REG, N. MARIANA ISLAN

P: 13OCT2020 127889 19.0N 147.0E 4.0-5.4 CAAAA No. Marianas

P: 18OCT2020 127889 16.0N 145.0E 4.0-5.3 ABAAA No. Marianas

NEIC reported this earthquake of M 5.2 in the northern Mariana Islands was felt with intensity II-III in the area(s) of the northern Mariana Islands at Saipan.

CENTRAL AND SOUTH AMERICA

O: 20OCT2020 08:33:27 10.9S 75.5W ML=4.1 EMSC CENTRAL PERU

P: 21OCT2020 127864 9.0S 80.0W 4.0-5.3 ABCAA No. Peru

NEIC reported this earthquake of M 4.8 in Southern Peru was felt with intensity II-III in the area(s) of Southern Peru at Acari, Arequipa.

O: 20OCT2020 21:37:21 13.6N 90.7W mb=4.4 EMSC OFFSHORE GUATEMALA

P: 19OCT2020 127880 13.0N 91.0W 3.5-5.2 AAAAA Guatemala

O: 20OCT2020 18:40:46 14.9N 94.0W ML=4.2 EMSC OFF COAST OF CHIAPAS, MEXICO

P: 19OCT2020 127877 14.0N 93.0W 3.5-5.1 AAAAA Chiapas, Mexico

O: 20OCT2020 16:54:44 15.4S 73.8W mb=4.8 EMSC SOUTHERN PERU

P: 19OCT2020 128044 14.0S 73.0W 4.0-5.3 ABAAA Central Peru

O: 21OCT2020 04:04:33 16.1N 95.3W ML=4.0 EMSC OAXACA, MEXICO

P: 21OCT2020 127877 17.0N 94.0W 3.5-5.0 AAAAA Chiapas, Mexico

O: 20OCT2020 08:46:16 17.2N 94.0W ML=4.0 EMSC VERACRUZ, MEXICO

P: 21OCT2020 127877 17.0N 94.0W 3.5-5.0 AAAAA Chiapas, Mexico

O: 20OCT2020 16:00:17 18.4N 68.9W ML=3.2 EMSC DOMINICAN REPUBLIC

P: 21OCT2020 127893 18.0N 67.0W 3.4-4.8 AABAA Puerto Rico

O: 20OCT2020 18:05:27 18.9N 70.1W ML=3.0 EMSC DOMINICAN REPUBLIC

P: 15OCT2020 127894 19.0N 71.0W 3.4-4.9 BAAAA Puerto Rico

O: 20OCT2020 23:48:54 18.9S 69.1W mb=4.0 EMSC TARAPACA, CHILE

P: 18OCT2020 128053 19.0S 69.0W 4.0-5.3 AAAAA So. Peru/Bolivia

O: 20OCT2020 19:01:42 19.1N 108.5W ML=4.1 EMSC REVILLA GIGEDO ISLANDS REGION

P: 20OCT2020 127879 19.0N 107.0W 3.5-5.1 AABAA Coast of Jalisco, Mexico

O: 20OCT2020 10:23:42 19.2N 67.3W Md=3.4 EMSC PUERTO RICO REGION

P: 18OCT2020 127900 20.0N 67.0W 3.0-4.4 AAAAA Bahamas/No. Caribbean

O: 21OCT2020 00:16:24 24.9N 109.3W ML=4.0 EMSC GULF OF CALIFORNIA

P: 18OCT2020 127903 24.0N 109.0W 3.5-4.8 BAAAA Gulf of California

O: 20OCT2020 11:13:39 38.0S 73.9W ML=4.0 EMSC OFFSHORE BIO-BIO, CHILE

P: 17OCT2020 128074 39.0S 73.0W 4.0-5.3 BAAAA Central Chile

AFRICA AND EUROPE

O: 21OCT2020 06:48:48 34.3N 25.2E ML=4.1 EMSC CRETE, GREECE

P: 19OCT2020 127928 35.0N 26.0E 3.0-4.4 AAAAA Crete