Abstract
The IMS infrastructure can be used effectively in civil applications, for instance to augment the capacity of organizations charged with warning the authorities about dangerous natural events, such as earthquakes and tsunamis. Relevant IMS data is already forwarded to regional tsunami centres under agreement with CTBTO. This includes seismic IMS stations for accelerated tsunamigenic event detection and hydroacoustic stations for the recording of the passage of the tsunami. In this work, we suggest that data from coastal and island T-stations is also useful for direct detection of the passage of the tsunami. The possibility of observing the passage of tsunamis on these coastal seismic stations was confirmed in the Pacific Ocean for the tsunamigenic Maule, Chile earthquake of 27 February 2010 on the horizontal components of two broad-band seismometers used as hydroacoustic T-station located on Socorro Island, Mexico. Similar observations of long period effects of the passage of tsunami on the horizontal components of near-shore seismometers had been made previously and tentatively explained as long-period components of the propagation modes of gravity waves, where the presence of the island is ignored. Polarization and amplitude analysis of the longperiod arrivals observed at Socorro allows an alternate physical explanation and our preferred explanation is that the islands strain field is responding elastically to the load of the very long wavelength tsunami on the walls of the island. This hypothesis is confirmed by analysis of the passage at Socorro of another tsunami from the September 29th, 2009, Samoa earthquake.