Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p34a..06p&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P34A-06
Mathematics
Logic
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5460] Planetary Sciences: Solid Surface Planets / Physical Properties Of Materials
Scientific paper
Impact structures are associated with distinct geophysical anomalies but the cause of the anomalies is not always obvious. In order to estimate which part of the anomalies is due to structural or tectonic origin, which part is due to post-impact sediments or water bodies and which part is caused by petrophysical properties, we carried out petrophysical measurements on impact and target rocks from eighteen impact structures occurring in crystalline target rocks. The impact rocks were split into five categories in order of decreasing shock pressure: melt, suevites, breccias, fractured and unfractured target rocks. This is a simplified division since every crater has unique characteristics. However, by doing it this way we will see the main trends in petrophysical properties vs. shock. The following properties were measured: bulk density, porosity, susceptibility, intensity of natural remanent magnetization (NRM) and Q-value. The data reveal distinct trends: 1. Porosity is decreasing from suevites to breccias to melts to fractured target up to unfractured targets, 2. Density is increasing in the same order, 3. The case for susceptibility is more complex: it appears that the susceptibility of the fractured target rocks is diminished from the original (unfractured target) value but no distinct trend is seen in other impact rock layers, 4. The NRM is also very variable and is case dependant, 5. the Q-value seems to decrease from suevites towards unfractured target rocks. The geophysical anomalies, in each case, also depend on the lithological type and strength of the target rocks among other things. Nevertheless, these petrophysical trends can be used to give some preliminary estimates of the "expected" gravity and magnetic anomalies. We will demonstrate with theoretical and real examples how the geophysical anomalies vary with variation in petrophysical data.
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