Mathematics – Probability
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31f..02l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P31F-02
Mathematics
Probability
[6022] Planetary Sciences: Comets And Small Bodies / Impact Phenomena, [6225] Planetary Sciences: Solar System Objects / Mars, [6250] Planetary Sciences: Solar System Objects / Moon, [7299] Seismology / General Or Miscellaneous
Scientific paper
Natural Impacts occurring on the surface of telluric planets are important seismic sources for constraining the crustal and upper mantle structure, especially when their impact location and impacting time can be determined by other complementing experiments, such as Earth based flash detection for the Moon or differential orbital imaging of the surface for Mars. When these complementary data are not available, which was the case of Apollo with the exception of artificial impacts, the location of impact as compared to quake is easier, as only their geographical location must be determined from seismic data. We present recent results of the analysis of impact related seismic data gathered by the Apollo Lunar seismic network during the 70th. By using the artificial impact, we first develop a calibrated analysis for extracting the impulse (i.e. mass time impact velocity) from the amplitude of seismic waves, and point out the effect of the generation of ejecta in the seismic impulse. This approach not only allows to constrain the mass of the impacts, but also to constrain the impact frequency-impactor mass relation. By combining both the Apollo long period and short period data, further analysis can be made on the dynamic of the seismic source. The combination of these date provides indeed broadband seismic analysis have been made allowing to constraint the seismic cut-off frequency and source spectrum associated with both natural and artificial impacts. We show that the source cut-off is, as compared to moonquakes, relatively low and around a few Hz for remotely detected impacts. It is also depending not only on the impact size, but also on the impact location, as the seismic radiation of the shock wave depends on the most-upper regolith layers. We finally use our results and forward modeling to prepare the GEMS seismic mission to Mars, considered by NASA for a launch in 2016. In order to have a robust estimation of the rates of seismic detection of impacts, we analyze and model the differences of seismic propagation properties between Mars and the Moon, and use this modeling to estimate the seismic response of impacts on Mars, as a function of both the impactor characteristics (mass and velocity) and epicentral distance. We then use statistical models of impactors, confirmed by both the Apollo seismic observations and the Mars Orbiter impacts observations, to estimate the present flux on Mars and to constrain the rate of seismic impact detection, as well as the expected probability to further locale these events by differential remote sensing. This analysis is performed by taking into account both the expected performances of the VBB seismometer of GEMS and the expected environmental noise after its deployment on the Martian surface. The perspectives in terms of crustal and upper mantle seismic imaging are finally provided in conclusion for both GEMS on Mars and SELENE2 on the Moon.
Banerdt B.
Garcia Raphaël F.
Gudkova T.
Kawamura Taichi
Kobayashi Nami
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