Understanding Extreme Geohazards: The Science of the Disaster Risk Management Cycle

European Science Foundation Conference
November 28 to December 1, 2011, Sant Feliu de Guixols, Spain

On the Complementary of High-Rate GPS and Strong-Motion Observations: A Case Study on the Near-Field Deformation Data for the 2011 Mw 9.0 Tohoku-Oki Earthquake

Rongjing Wang
GeoForschungsZentrum Potsdam, Germany, wang@gfz-postdam.de

Near-field ground motion data are available nearly in real time either from modern strong-motion or continuous GPS networks, allowing robust solutions for earthquake source parameters, and in particular, for rapid disaster assessment and early warning. Such wide applications require the data to cover a very broad frequency band. The strong-motion sensors provide ground acceleration with high resolution at high frequency. The velocity and displacement can be obtained in principle by integrating over time. Unfortunately, the raw strong-motion records include generally time-dependent baseline errors. In most cases, it is impossible to retrieve the real ground velocity and displacement from the strong-motion records without a reliable correction for the baseline errors. So far, such correction can only be made empirically with unknown uncertainties. Conversely, the GPS derived displacement has high accuracy for low frequencies, but due to the large high-frequency noise, velocity and acceleration obtained after differentiation are less accurate than that from seismic sensors. This paper presents a case study on the 2011 Mw 9.0 Tohoku-Oki earthquake, showing how the near-field ground motion information from the geodetic and seismic equipments is complementary, therefore suggesting their joint use particularly when the network coverage is sparse. First the strong-motion records from the K-Net and KiK-Net are analysed using an automatic empirical baseline correction tool. The static coseismic displacement data are obtained by double integration and then used to derive the permanent slip distribution. Comparisons with the corresponding GPS based solutions yield a quantitative estimation of uncertainties of the empirical baseline correction. Furthermore, a dozen nearby GPS and strong-motion station pairs are selected for comparisons between their displacement and velocity time series. Finally, a new approach is proposed to combine the complementary ground motion information from the individual observation systems.