There are several ways to calculate earthquake magnitude. The best one (moment magnitude) of course takes the longest to calculate & sometimes needs human review before it goes out. So, in the interest of speed, you get the slightly less accurate ones first & the better one a few minutes later. In this magnitude range (around 5 to 5.5) it usually turns out to be a "downgrade".
Hope this helps.
One or two TV stations have recording drums, but I don't think any way to calculate their own locations or magnitudes. So they look at the USGS web site just like everyone else. If they don't keep looking at it, their news may be old.
Kate
On Wed, Jul 7, 2010 at 9:16 PM, newnethboy <kef413@gmail.com> wrote:
I always go to the site I listed, which is USGS (if we can't trust them,
whom can we trust). Within a minute or so of the quake, they had up a
listing (all automated) showing location and a magnitude of 5.9. About 15
minutes later, a human had reviewed it, and (based on further readings, I
presume) amended the magnitude to 5.4.
Meanwhile, I presume, the TV stations read their seismometers (which may
vary in accuracy, and don't take into account multiple readings), and gave
the numbers from their instruments.
Then there's the issue of communications delays. It's entirely likely some
reporters were telling audiences "5.9" even as the posting was changed to
5.4.
And all this is before the factors that April described.
----- Original Message -----
From: "Ivy" <navy10452002@yahoo.ca>
To: <californiadisasters@yahoogroups.com>
Sent: Wednesday, July 07, 2010 5:39 PM
Subject: Re: [californiadisasters] Fw: [California's Earthquake Forum] 5.9
13 mi NNW from Borrego Springs S. CA
When do you get the official strength of the quake ? Right now the reports
are
from 5.3 to 5.9
what was the official strenght?
*canadianandamericanissues@yahoogroups.com*
*Free-ThinkersClub@yahoogroups.ca*- the other view
Ivy
________________________________
From: newnethboy <kef413@gmail.com>
To: californiadisasters@yahoogroups.com
Sent: Wed, July 7, 2010 5:24:56 PM
Subject: Re: [californiadisasters] Fw: [California's Earthquake Forum] 5.9
13 mi
NNW from Borrego Springs S. CA
Now (1709) listed as 5.4 on
http://earthquake.usgs.gov/earthquakes/recenteqsus/Maps/special/California_N
evada_eqs.php
----- Original Message -----
From: "Hardin Rich" <hardinrich@sbcglobal.net>
To: <WorldEarthquakes@yahoogroups.com>
Cc: <californiadisasters@yahoogroups.com>
Sent: Wednesday, July 07, 2010 5:07 PM
Subject: [californiadisasters] Fw: [California's Earthquake Forum] 5.9 13 mi
NNW from Borrego Springs S. CA
a.. This event has been reviewed by a seismologist.
Magnitude 5.9
Date-Time a.. Wednesday, July 07, 2010 at 23:53:33 UTC
b.. Wednesday, July 07, 2010 at 04:53:33 PM at epicenter
Location 33.417°N, 116.483°W
Depth 11.7 km (7.3 miles)
Region SOUTHERN CALIFORNIA
Distances a.. 22 km (13 miles) NNW (332°) from Borrego Springs, CA
b.. 23 km (14 miles) SE (131°) from Anza, CA
c.. 33 km (20 miles) NE (52°) from Lake Henshaw, CA
d.. 41 km (25 miles) SW (215°) from Indio, CA
e.. 45 km (28 miles) S (174°) from Palm Springs, CA
f.. 94 km (58 miles) NE (41°) from San Diego, CA
Location Uncertainty horizontal +/- 0.3 km (0.2 miles); depth +/- 0.6
km (0.4 miles)
Parameters Nph=122, Dmin=10 km, Rmss=0.26 sec, Gp= 29°,
M-type=local magnitude (ML), Version=3
Source a.. California Integrated Seismic Net:
b.. USGS Caltech CGS UCB UCSD UNR
Event ID ci10736069
a.. Did you feel it? Report shaking and damage at your location. You can
also view a map displaying accumulated data from your report and others.
Earthquake Maps
a..
Earthquake Location
b..
Google Map
c..
Google Earth KML
(Requires Google Earth)
d.. Did you feel it? Report shaking and damage at your location. You can
also view a map displaying accumulated data from your report and others.
Scientific & Technical Information
a.. Waveforms
Additional Information
a.. CALTECH/USGS AFTERSHOCK PROBABILITY REPORT
b.. 24-hour Aftershock Forecast Map
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