Preliminary Analysis of the CASES GPS Receiver Performance during Simulated Seismic Displacements

Abstract:

We explore the ability of a new GPS software receiver, called CASES

(Connected Autonomous Space Environment Sensor), to measure seismic

displacements in realtime. Improvements in GPS technology over the last 20 years allow for precise

measurement of ground motion during seismic events. For example, GPS data has been used to

calculate displacement histories at an earthquake’s epicenter and fault slip estimations with great

accuracy. This is supported by the ability to measure displacements directly using GPS, bypassing

the double integration that accelerometers require, and by higher clipping limits than seismometers.

The CASES receiver developed by ASTRA in collaboration with Cornell University and the

University of Texas, Austin represents a new geodetic-quality software-based GPS

receiver that measures ionospheric space weather in addition to the usual navigation

solution. To demonstrate, in a controlled environment, the ability of the CASES receiver to measure

seismic displacements, we simulated ground motions similar to those generated during earthquakes,

using a shake box instrumented with an accelerometer and a GPS antenna. The accelerometer

measured the box’s actual displacement. The box moved on a manually controlled axis that

underwent varied one-dimensional motions (from mm to cm) at different frequencies and

amplitudes. The CASES receiver was configured to optimize the accuracy of the position solution. We

quantified the CASES GPS receiver performance by comparing the GPS solutions against the

accelerometer data using various statistical analysis methods. The results of these tests

will be presented.

The CASES receiver is designed with multiple methods of accessing the data in realtime,

ranging from internet connection, blue-tooth, cell-phone modem and Iridium modem. Because

the CASES receiver measures ionospheric space weather in addition to the usual navigation

solution, CASES provides not only the seimic signal, but also the ionospheric space weather

effects produced by the seismic signal and by tsunamis, including signatures of acoustic waves and

gravity waves in the ionosphere. Examples of CASES GPS receiver data containing ionospheric

space weather signatures generated by Pacific Rim earthquakes and tsunamis will be also presented.