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23011 |
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Date: September 18, 2023 at 06:23:50
From: Mikhail, [DNS_Address]
Subject: NorCal M6.2 +/- 0.2 on 10/1 +/- 3d (Pacific time) |
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PREDICTED TIME: Sunday, Oct. 1, 2023,
Noon Pacific Time, ± 72 hours
(mainshock only, aftershocks* are
irrelevant to this prediction).
PREDICTED MAGNITUDE: 6.0 – 6.4
(moment magnitude, USGS).
PREDICTED LOCATION: Within California
W of 120° and N of 36° (including offshore to
edge of continent).
PROBABILITY of hitting all parameters by random
coincidence: ~0.16% (chance of success: 1 in ~600)
based on prior 100-year EQ history (USGS)
NO CONFIDENCE LEVEL PROVIDED -- INSUFFICIENT TRACK
RECORD.
* Arbitrary “aftershock” definition: An earthquake
preceded by a larger earthquake within one geocentric
degree (111 km) and within one year (to the hour).
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Responses:
[23012] [23015] [23032] |
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23012 |
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Date: September 18, 2023 at 13:44:14
From: Skywise, [DNS_Address]
Subject: Re: NorCal M6.2 +/- 0.2 on 10/1 +/- 3d (Pacific time) |
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My probability results are a little better than yours.
I get a 1 in 438 chance, or about 1.37%.
Below are the quakes I used for my calculations, which is the Jones probability method.
------- Filter settings -------
Start date: 1923/01/01T00:00:00.000000 - 2423420.500000
End date: 2023/09/18T23:59:59.999999 - 2460206.500000
Event types: 1
all
North lat: 42.000000
South lat: 36.000000
West lon: -125.000000
East lon: -120.000000
Radius: 0.000
Min mag: 6.000
Max mag: 6.400
Min depth: -10.000
Max depth: 1000.000
-------------------------------
Event ID Date/Time Latitude Longitude Depth Mag Event Type
ushis718 1925/06/04T12:02:52.000000 41.50000000 -125.00000000 -99.9000 6.000 earthquake
ushis750 1926/10/22T12:35:00.000000 36.61700000 -122.35000000 -99.9000 6.100 earthquake
iscgem910175 1926/10/22T13:35:27.000000 36.72500000 -122.18000000 10.0000 6.300 earthquake
iscgem906203 1932/06/06T08:44:26.000000 40.73000000 -124.21100000 15.0000 6.400 earthquake
ushis1643 1948/12/29T12:53:28.000000 39.55000000 -120.08000000 -99.9000 6.000 earthquake
iscgem894786 1951/10/08T04:10:38.000000 40.23800000 -124.71300000 15.0000 6.000 earthquake
iscgem893449 1952/09/22T11:41:29.000000 40.23400000 -124.32200000 15.0000 6.000 earthquake
iscgem879414 1960/06/06T01:17:53.000000 40.72900000 -124.79200000 15.0000 6.000 earthquake
nc1032447 1976/11/26T11:19:32.070000 41.03516670 -124.94966670 41.7800 6.300 earthquake
nc17204 1984/04/24T21:15:18.760000 37.30966670 -121.67883330 8.1930 6.200 earthquake
nc228027 1991/08/17T19:29:40.000000 40.25166670 -124.28583330 8.3200 6.000 earthquake
nc72282711 2014/08/24T10:20:44.070000 38.21516670 -122.31233330 11.1200 6.020 earthquake
nc73666231 2021/12/20T20:10:31.310000 40.39016670 -124.29800000 27.0400 6.200 earthquake
nc73821036 2022/12/20T10:34:24.770000 40.52500000 -124.42300000 17.9100 6.400 earthquake
Total records listed: 14
Time to complete function: 00:00:05.380131
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Responses:
[23015] [23032] |
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23015 |
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Date: September 18, 2023 at 20:47:23
From: Mikhail, [DNS_Address]
Subject: Re: NorCal M6.2 +/- 0.2 on 10/1 +/- 3d (Pacific time) |
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Thanks for checking, Skywise!
You included the following events – I should have
counted them:
1926/10/22T12:35:00 – it was a foreshock (by 16
seconds). So, not an aftershock.
2022/12/20T10:34:24 M6.400 – although within one year
after the nearby 2021 event, that 2021 event was M6.2.
So, the 2022 M6.4 was not an aftershock.
You included the following – I intentionally ignored
them:
1926/10/22T13:35:27 M6.300 – it followed 1926-10-
22T12:35:16.170Z which was M6.35 according to the USGS
as of last night. So, the M6.300 event was an
aftershock by my definition.
1932/06/06T08:44:26 M6.400 – it was M6.45 according to
the USGS as of last night. So, rounded up, was above my
magnitude window of M6.4.
1952/09/22T11:41:29 M6.000 – it was within one year
after the adjacent 1951/10/08T04:10:38, which M6.02
according to the USGS as of last night. So, an
aftershock by my definition.
1960/06/06T01:17:53 M6.000 – it was within one year
after, and smaller than, a nearby M6.3 on 1959/07/23.
So, an aftershock by my definition.
Summary:
I ignored 4 events that you included because they were
aftershocks by my definition or outside my magnitude
window.
I should have counted 2 events that you included,
because I erred.
My net count of mainshocks within the past 100 years,
therefore, should be adjusted up from 10 to 12.
My corrected probability should be:
12 eq / 100 yr
12 eq / 36525 dy = 0.000329 eq / dy
P(6-day period) = 6 x 0.000329 = 0.00197 = ~0.2%
A 1 in ~500 chance and sufficiently remote for my
purposes.
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Responses:
[23032] |
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23032 |
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Date: September 30, 2023 at 13:35:53
From: Mikhail, [DNS_Address]
Subject: Re: NorCal M6.2 +/- 0.2 on 10/1 +/- 3d (Pacific time) |
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Intraplate foreshocks? (Assuming the top of the Gorda
Plate is ~15 km deep at the coast.)
M 4.2 - 15 km SW of Ferndale, CA
2023-09-30 17:16:48 (UTC)
40.498°N 124.405°W
26.3 km depth
M 4.7 - 3 km SW of Ferndale, CA
2023-09-30 15:26:26 (UTC)
40.559°N 124.289°W
17.9 km depth
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Responses:
None |
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