Investigation of 3-D lateral variations on seismic waveform modeling, in preparation for the InSight mission to Mars

Abstract:

In 2016, the InSight mission will provide the very first seismic records from Mars after installing a seismometer on the surface of the Red Planet. Obtaining information on the deep 1-D seismic structure of Mars using a single geophysical station will be challenging. However, successful test inversions using body and surface waves have been presented in a preliminary study by Panning et al. (2015). Future investigations need now to focus on inversions making a complete use of the seismic waveform. An important challenge is to investigate the effects of 3-D lateral variations of seismic velocity structures on seismograms. The HOPT (Higher Order Perturbation Theory) code originally developed by P. Lognonné and E. Clévédé (Lognonné, 1991 ; Lognonné and Clévédé, 2002) and based on the perturbation theory allows for the computation of synthetic seismograms in a 3-D Earth. We adapted the code for Mars and computed surface wave synthetics in a 3-D planet, initially only considering the effects of the planet's ellipticity as well as the lateral variations in the depth of the Moho which are known through gravity measurements (e.g. Neumann et al., 2004). Additional constraints from lateral variations in topography will be the focus of future work. These synthetics can be compared to future seismic data in order to identify a suite of Martian internal structure models that best match the data. To do so, we first need to estimate the resolvable parameters concerning the Mars deep interior while considering the 3-D effects, which is the main goal of this study. Furthermore, in preparation for the InSight mission data return phase, the computation of these synthetic (but realistic) seismograms is primordial to test the softwares developed by the InSight Mars Quake and Mars Structure Services (in charge of locating the seismic events, and using them to assess the internal structure of Mars).