Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p51a0914b&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P51A-0914
Other
5430 Interiors (8147), 5450 Orbital And Rotational Dynamics (1221), 6250 Moon (1221), 7299 General Or Miscellaneous
Scientific paper
One of the first-recognized results from the Apollo lunar seismic experiment was the observation of deep moonquakes occurring with monthly (tidal) periodicity. Despite this early insight, the physics of the process is still poorly understood. Previous studies have investigated relationships among tidal stress and moonquake occurrence times, amplitudes, and polarities, but conclusions regarding fault geometry, the role of ambient stress, and the identification of relevant stress tensor terms differ. In addition, there has been relatively little examination of any deep event source other than A1 (the largest, at 323 events). Our objective is to obtain a better understanding of tidal effects on lunar seismicity, through three new avenues of investigation: (1) integration of our discovery of additional moonquakes, (2) development of improved models of the tidal potential, and (3) exploitation of recent advances in terrestrial seismic triggering, both by tides and other quakes. We have recently developed a cross-correlation technique that allows identification of new moonquakes in the continuous Apollo seismic data. During the original event identification process, the continuous data were examined in detail, by eye, only around those tidal periods suspected to be important to moonquake occurrence. Our method provides an objective detection process for events as it searches automatically through the entire continuous data set. This has resulted in an average 30% increase in the number of events for the five largest groups; the new events exhibit the same tidal periodicities present in the original events. We will explore the extent to which normal, shear and Coulomb stresses resolved on fault planes of specified orientation provide robust diagnostics for the times, polarities, and amplitudes of moonquakes for the five largest clusters. Our predicted stresses use a formulation for the tidal potential based on the JPL planetary ephemeris. Also we hope to better characterize the various moonquake sources using our new events, in particular to discriminate between fixed and time-varying sources.
Bills Bruce G.
Bulow R. C.
Johnson Clifton L.
Shearer Peter M.
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