Long-period seismology on Europa: 2. Predicted seismic response

摘要

Previous studies have documented the potential for using relatively short-period body waves and intermediate-period surface waves to explore the structure and tectonics of Europa. We show that long-period measurements (0.001 to 0.1 Hz) may have large amplitudes of displacement (millimeters to centimeters) and are potentially measurable from orbit without requiring a lander. To accurately model the long-period response of Europa, we use normal modes calculated from physically self-consistent models of Europa's structure developed in part 1 (Cammarano et al., 2007). On the basis of the geometry of observed faults, we estimate that faulting events of magnitude 5 or larger may occur regularly. Synthetic seismograms show that long-period displacement measurements with millimeter accuracy could detect current tectonic activity and determine the thickness of Europa's ice shell, and confirm the presence of a subsurface ocean. Determination of deeper structure with seismic measurements, however, is more challenging in the presence of a global liquid ocean, which acts to decouple deeper seismic energy from the surface. Copyright 2006 by the American Geophysical Union.