From: Michael B. Heflin
Date: 8 Jan 1996 17:21:32 
Subject: [SCIGN-0139] Possible rate change at JPLM after Northridge earthquake. 

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SCIGN Electronic Mail    Mon Jan  8 17:21:32 PST 1996      Message Number 0139
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Author: Michael B. Heflin
Subject: Possible rate change at JPLM after Northridge earthquake.

Co-seismic displacements at JPLM caused by the Northridge earthquake were
provided by Zumberge and Bock et al. in IGS messages 455 and 457 respectively. 

IGSMAIL 455
north    -0.64 +/- 0.32 cm
east      0.68 +/- 0.23 cm
vertical -0.29 +/- 0.80 cm

IGSMAIL 457
North: -5.1 mm +- 3.2 mm
East:   6.5 mm +- 3.9 mm
Up:    -2.0 mm +- 6.4 mm

Data since the Earthquake indicate that the velocity of JPLM has changed.  A
table of the numbers is given below.

 Coeseismic offsets in mm.  New - Old
 N   94JAN17           -8.4  +-      0.4
 E   94JAN17            7.9  +-      1.0
 V   94JAN17           -4.6  +-      2.4

 Rate Changes in mm/yr.     New - Old
 N  94JAN17         -4.2145  +-       .6354
 E  94JAN17         19.7099  +-      1.6765
 V  94JAN17         12.0286  +-      3.6929

There were some equipment alterations at JPLM which suggest these numbers be
used with caution but as more data are added the rate change looks increasingly
significant.  It is not observed at other sites such as GOLD or ALGO.  I would
be interested to hear if there are any models which predict such a rate change.
The time series can be viewed at http://sideshow.jpl.nasa.gov/mbh/series.html.


[Mailed From: mbh@cobra.jpl.nasa.gov]