Temporal and spatial properties of some deep moonquake clusters

Abstract

Using the event search method of Bulow et al. (2005), we have found 503 new deep moonquakes among the eight largest (in terms of total number) nearside source regions, increasing the number of identified events for each cluster an average of 36% over the existing catalog. These new events provide an improved deep event catalog, with which we explore some temporal and spatial aspects of deep moonquakes. First, we examine the spectra of moonquake occurrence times at each deep source region, and observe known tidal periodicities, notably those at ∼27 days and 206 days. Application of spectral methods for the analyses of point processes (discrete events) allows us to resolve closely spaced tidal periods not previously seen in moonquake data. Second, we pick seismic phase arrival times from optimized stacks of events from each source region. We use these picks, along with published velocity models, to relocate the nine source regions. Source regions A1 and A18 are the best located, with 95% confidence bounds of less than ±5° in latitude and longitude, and consistent with estimates from different studies. The locations of source regions A8 and A9 are poorly constrained, with uncertainties in latitude of up to ±28° resulting from the absence of clear phase arrivals at station 15. Large trade-offs exist between relocation estimates and choice of velocity model, and the lack of reliable seismic phase arrivals severely affects location error. Copyright 2007 by the American Geophysical Union.