Una strategia semplice per la GPS Seismology e i sistemi di early warning per gli tsunami denominata VADASE

Abstract

I recenti avvenimenti legati al fortissimo terremoto avvenuto in Giappone lo scorso 11 marzo 2011 e al tragico e devastante tsunami ad esso conseguente hanno, una volta di più, posto all'attenzione della comunità  internazionale la necessità  di disporre sistemi di early warning per gli tsunami sempre più efficienti. I sistemi GNSS, se utilizzati in modo adeguato, possono dare un grande contributo come nel caso della tecnica VADASE qui esposta.

Co-seismic Displacement Estimation. Improving Tsunami Early Warning Systems

The great earthquake (M=9.0) which hit the Island of Honshu (Japan) on March 11, 2011 and generated a tremendous tsunami raised once more the attention towards tsunami early warning systems.In this respect, during the last years, several studies demonstrated that GPS can be used effectively for estimating coseismic displacement waveforms (so called GPS seismol-ogy), with accuracies ranging from a few millimeters to a few centimeters. These stud-ies were mainly developed off-line, re-analysing the GPS data acquired during strong earthquakes and well known processing strategies (Precise Point Positioning and In-dependent Positioning) were developed to lower the latency between the earthquake occurrence and the coseismic displacement waveforms estimation as much as possible. In this regard, during the Real Time GPS Science Requirements Workshop held in Sep-tember 2007 in Leavenworth (Washington, USA) the goal of achieving 1 cm real-time GNSS displacement accuracies in the global reference frame within 3 minutes following an earthquake was adopted.It is in this frame that here we present a novel approach named VADASE, with which we are able to estimate accurate co-seismic displacement waveforms in real-time, just using the standard broadcast products (orbits and clocks) and the high-rate (1Hz or more) carrier phase observations continuously collected by a GPS receiver. Since no other data than those routinely collected by a stand-alone GPS receiver are needed the algorithm can, in principle, be directly embedded into the receiver firmware.VADASE was recognized a simple and promising approach towards the fulfillment of the mentioned goal and it was awarded with the DLR Special Topic Prize and with the First Audience Award within the European Satellite Navigation Competition 2010.The effectiveness of VADASE is here shown through its application to the Baja California (Mexico) earthquake (Mw=7.2, April 4, 2010) and to the great Honshu (Japan) earth-quake (M=9.0, March 11, 2011).