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Posted by Lowell on August 23, 2001 at 16:49:01:
The largest earthquakes in the U.S. and the World today were apparently
far-field aftershocks from the New Zealand Mw 7.0 earthquake of 21 August. The largest event of the day occurred in the Bismarck Sea north
of Papua, New Guinea. This earthquake is initially given a Mb
5.6, however initial seismograms suggest the magnitude could be
larger. The forecast for this event had quality AAAAA if local
(PNG) time is used. It occurs at 45 degrees from the New Zealand
earthquake and appears to be a far-field aftershock. The forecast
had noted:
"43-45 degrees: Papua New Guinea, BISMARCK SEA"
and
"Areas which have had several occurrences of unusual earthquakes
following such events include: ...
Papua New Guinea/New Britain" The last event within 200 km of this epicenter which had Mb>5.5
was on August 26, 1999 (Mw 6.6) and was probably a far-field aftershock
of the great destructive Izmit Turkey earthquake of August 17, 2001
as it lies near the shadow zone boundary from that event (103-108 degrees). The parameters (NEIS) of this earthquake are currently: 2001/08/23 21:45:08.1 3.1S 146.3E 33G Mb5.6 NEIA BISMARCK SEA Seismograms can be viewed at URL below:
http://aslwww.cr.usgs.gov/Seismic_Data/heli2.htm U.S./CANADA The largest event of the day in the U.S. occurred in eastern Wyoming.
This was the fourth event in this region in the past 24 hours.
These earthquakes were anticipated in the far-field aftershock
forecast from New Zealand as they fall at the p- and s- wave
shadow zone boundary where seismic energy is concentrated by
internal earth reflections and refractions off the core-mantle
boundary of p- and s-waves. With the exception of the antipode
this is the area where far-field triggering is expected to be
greatest. The parameters (NEIS) of these earthquakes are: 23AUG2001 18:35:57 41.8N 108.8W ML=3.4 UUSN ENE of Superior, WY
23Aug2001 18:48:16 41.6N 108.8W ML=3.3 NEIS EASTERN WYOMING
23Aug2001 20:06:32 43.3N 106.2W ML=2.6 NEIS EASTERN WYOMING
22Aug2001 21:18:33 41.8N 108.6W ML=2.7 NEIS EASTERN WYOMING The far-field forecast from New Zealand had stated regarding
the possibility of these events: "103-106 degrees***: ..... central Plains U.S" This is the strongest activity in the area in more than a year. Unusual earthquakes were also recorded in Maine (Ml 2.3) and
Nova Scotia today. It appears the far-field triggering effects
from the New Zealand event may be considerable.
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