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VADASE: A GPS Contribution to Earthquake Studies

Por: | 04 de noviembre de 2013

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By Gabriele Colosimo, University of Rome, La Sapienza

Image: Displacements at MIZU station (Japan) over the interval 05:46:10-05:50:10, 11 March 2011. (Tohoku-oki earthquake, MW = 9.0)

In recent years, several researches have demonstrated the effective use of GPS in studying earthquakes. VADASE, developed at the University of Rome La Sapienza, today provides a real cost-effective solution.

Since the early 2000s, GPS has been effectively used to contribute in earthquake studies. Geodesy and Geomatics Area (AGG) of Sapienza University of Rome recently developed a brand new real-time approach, named VADASE (Variometric Approach for Displacements Analysis Stand-alone Engine), to detect the displacements of a GPS receiver. Eventually, VADASE was appointed as a powerful tool to monitor earthquakes' damages and to raise early tsunami warnings. The algorithm was applied to assess many recent global earthquakes, including the one in northern Italy (which occurred on 20 May 2012, Emilia Romagna).

In July 2009, I was having lunch with Prof. Mattia Crespi and Dr. Augusto Mazzoni in a restaurant close to Sapienza Engineering Faculty. For the first time, we discussed a new approach to estimate in real-time the movements of a GPS receiver and we used the paper tablecloth to write the preliminary equations. Three years later those tablecloth scribblings testify of the first step towards the realization of VADASE, a brand-new algorithm to estimate in real-time the co-seismic displacement waveforms induced by an earthquake.

Global Navigation Satellite Systems (GNSS), like the Global Positioning System (GPS), are nowadays very well known. GPS was originally set up by the Department of Defense (DoD) of the United States for military purposes. Things changed on 1 May 2000, when U.S. president Bill Clinton by “pushing a button” tore down the position accuracy to less than 10 meters, giving birth to the commercial development of GPS technology. Today, the GPS industry is worth billions of dollars; almost any new smart phone or car has an embedded GPS receiver (which costs just a few hundreds of dollars) for navigation purposes, and there are countless Information Systems (Google Earth, Microsoft Virtual Earth, etc.) that describe reality within a global reference frame that GPS contributed to.

In recent years, several researches have demonstrated the effective use of GPS in studying earthquakes. It is the so-called GPS seismology, which aims to exploit GPS to contribute in the estimation of important seismic parameters (for example, seismic moment and magnitude MW). In particular, some key features distinguish GPS with respect to other well-known seismological instruments (like seismometers and accelerometers). At first, seismometers returned either velocities or accelerations and one needed to operate mathematical integration(s) to achieve the instrument positions. Instead, GPS now returns directly positions, which are essential to seismic assessment. Secondly, the high energy released by strong earthquake can corrupt the acquisition capabilities of seismometers located in the vicinity (up to a thousand km) of the epicenter in what is known as the saturation problem. Instead, even though GPS is less sensitive than seismometers, it does not saturate, not even for very strong earthquakes.

GPS seismology was effectively used to assess many recent global earthquakes (for example, Alaska 2002 MW 7.9, Chile 2010 MW 8.8, California 2010 MW 7.2). In July 2009 we started to develop a new approach to contribute to GPS seismology with the aim of accurately estimating the displacements caused by an earthquake in real-time and using a single receiver (possibly a low-cost one). As a matter of fact, these requirements were not met by the two most common strategies used in GPS seismology so far: Precise Point Positioning and differential positioning. At present, VADASE is the only approach capable of using a single GPS receiver to obtain real-time displacements, with a few centimeters accuracy level. Moreover, the algorithm requires no powerful hardware and can be embedded in the receiver firmware. Simple transmission equipment can be added to allow communication if a defined displacement's threshold is exceeded. With such a configuration, in case an earthquake occurs, the displacements can be retrieved in real-time and immediately transmitted to a remote control center, which can decide whether or not to raise a tsunami alert.

VADASE is subject to a pending patent of Sapienza University ever since June 2010. In October 2010 it was recognized as a simple and effective approach towards real-time seismic displacement estimation and was awarded the DLR (German Aerospace Agency) Special Topic Prize and the First Audience Award in the European Satellite Navigation Competition 2010. VADASE's effectiveness was internationally recognized during the tremendous earthquake in Japan (March 2011, MW = 9.0), when AGG research team was able to provide the first displacement results among the scientific community.

After the earthquake that caused so much damage in northern Italy, Italian Civil Protection Agency proposed to deploy a monitoring campaign in order to evaluate seismic dangerousness for strategic interests buildings. Thanks to the real-time capabilities provided by VADASE, for the first time ever GPS was considered a worthy instrument to join seismometers in order to achieve the proposed goal.

Considering all its positive results, we hope that VADASE will provide an effective contribution to tsunami warning systems and that the possibility to work with low-cost receivers will lift up the application of GPS (and possibly of other GNSS like GLONASS (Russian), GALILEO (European) and Compass/Beidou (Chinese), in an interoperability framework) as an earthquake monitoring device.

In times of economic crisis and budget cuts that do not leave the Research and Development sector unaffected, VADASE looks like much more than just a second-best option.


Gabriele Colosimo
University of Rome, La Sapienza

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