Analysis of seafloor seismograms of the 2003 Tokachi-Oki earthquake sequence for earthquake early warning

Jeffrey J McGuire

Department of Geology and Geophysics
Woods Hole Oceanographic Institution
Woods Hole MA 02543, USA

Frederik J Simons

Geosciences Department
Princeton University
Princeton NJ 08544, USA

John A. Collins

Department of Geology and Geophysics
Woods Hole Oceanographic Institution
Woods Hole MA 02543, USA

Abstract

Earthquake Early Warning (EEW) algorithms estimate the magnitude of an underway rupture from the first few seconds of the P-wave to allow hazard assessment and mitigation before the S-wave arrival. Many large subduction-zone earthquakes initiate 50-150 km offshore, potentially allowing seafloor instruments sufficient time to identify large ruptures before the S-waves reach land. We tested an EEW algorithm using accelerograms recorded offshore Hokkaido in the region of the 2003 Mw 8.1 Tokachi-Oki earthquake and its aftershocks. A wavelet transform of the first 4 seconds of the P-wave concentrates information about earthquake magnitude from both waveform amplitude and frequency content. We find that wavelets with support of a few seconds provide discriminants for EEW that are both accurate enough to be useful and superior to peak acceleration or peak velocity. Additionally, we observe a scaling of wavelet coefficient magnitude above Mw 6.0 indicating that, at least for the mainshock and largest aftershock (Mw 7.1), the final size of a rupture could have be estimated in a stochastic sense from the initial portion of the seismogram.

Figures

1. Figure 01 Representative waveforms (not included in paper)
   
2. Figure 02 Representative waveforms and wavelet analysis
   
3. Figure 03 Which is better: wavelets, peak velocity or acceleration?
   
4. Figure 04 Wavelet correlates with magnitude as the Sato-Hirasawa model
   

Frederik Simons