Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Los Angeles Squeeze

[Subject Prev][Subject Next][Thread Prev][Thread Next]

Mr. Chris, I understand your doubts, the accuracy of only one  pair of
receivers is only within 1 centimeter (one Sation Base of a well Know
positition and a mobile) , remember that you have a Net of 60 receivers
with a Net of Control of well know position, this Net of control is very
far of the zone of movement ,so you  can make differential corrections,
if you have a Net  of 60 receivers you can correct the accuracy of all
the Net as low as 1 millimeter.

Serroels, Chris/SAC wrote:

> One more question:
> How do you measure a 1/2 centimeter movement when they state
> that the accuracy of the technology is only within 1 centimeter.
> -----Original Message-----
> From: Bill Allen, S.E. [mailto:Bill(--nospam--at)]
> Sent: Thursday, October 29, 1998 5:20 PM
> To: seaint(--nospam--at)
> Subject: RE: Los Angeles Squeeze
> Just one question:
> How can the "results" come from "250 *planned* GPS receivers"?
> Regards,
> Bill Allen
> -----Original Message-----
> From: Yank2002(--nospam--at) [mailto:Yank2002(--nospam--at)]
> Sent: Thursday, October 29, 1998 4:40 PM
> To: seaint(--nospam--at)
> Subject: Los Angeles Squeeze
> PASADENA, CALIFORNIA 91109.  TELEPHONE (818) 354-5011
> Contact:  Mary Hardin, (818) 354-0344
> FOR IMMEDIATE RELEASE                         October 28, 1998
>      Downtown and West Los Angeles are moving toward the San
> Gabriel Mountains and the metropolitan area in between is being
> and will be squeezed slowly over the next several thousand years,
> according to researchers using precise satellite surveying
> techniques at NASA's Jet Propulsion Laboratory (JPL), Pasadena,
> CA.
>      The measurements suggest that new mountains may be forming
> to the south of the high San Gabriel Mountains.
>      The results come from the Southern California Integrated
> Global Positioning System (GPS) Network, an array of 60 current
> and 250 planned GPS receivers that continuously measures the
> constant, yet tiny, movements of earthquake faults throughout
> Southern California.
>      "We've known for some time that the area between the
> coastline and the Mojave Desert is being squeezed together by the
> constant movement of Earth's crust," said Dr. Donald Argus, a
> geophysicist at JPL.  "This new research helps pinpoint the area
> that's being squeezed. Specifically, downtown and West L.A.
> appear to be moving toward the San Gabriel Mountains at about
> half a centimeter (one-fifth of an inch) per year."
>      Argus is presenting his finding Oct. 29 at the annual
> meeting of the Geological Society of America in Toronto, Canada.
>      "While this research does not mean that an earthquake in Los
> Angeles is imminent, one possible conclusion is that the
> earthquakes that occur in Los Angeles might be concentrated in
> the northern part of the basin," Argus said.
>      The GPS surveying system uses radio signals transmitted from
> a constellation of 24 Earth-orbiting satellites that are jointly
> operated by the U.S. Departments of Defense and Transportation.
> Equipment on the ground receives signals from several satellites
> at a time, allowing scientists to pinpoint the position of a
> receiver to better than 1 centimeter (0.4 inch).
>      "The regional project is designed for exactly this kind of
> study.  Our goal is to observe and monitor the slow, small
> motion, called strain, of the ground in greater Los Angeles,"
> said JPL's Dr. Frank Webb, chair of the Southern California
> network.  "This research helps us learn where earthquakes are
> more likely to happen, and helps with estimating the regional
> earthquake hazard in Southern California.  It enables other
> agencies to make priorities about earthquake mitigation
> activities, including emergency preparedness and retrofit
> strategies."
>      There are now about 60 GPS receivers on the ground around
> Southern California with two new sites being added every week.
> The earthquake network began in 1990 with only four GPS receivers
> as a prototype project funded by NASA.  It detected very small
> motions of Earth's crust in Southern California associated with
> other California earthquakes in June 1992 in the town of Landers
> and in January 1994 in Northridge.
>      The Southern California network includes a number of
> institutions using GPS for earthquake research. The consortium is
> coordinated by the Southern California Earthquake Center, a
> National Science Foundation science and technology center
> headquartered at the University of Southern California. The array
> is operated by JPL, USC, the U.S. Geological Survey and the
> Institute of Geophysics and Planetary Physics at the University
> of California at San Diego's Scripps Institution of Oceanography.