Regional Body-Wave Attenuation Using a Coda Source Normalization Method: Application to MEDNET Records of Earthquakes in Italy

Journal Article · Thu Feb 01 04:00:00 EST 2007 · Geophysical Research Letters

DOI:https://doi.org/10.1029/2007GL029990· OSTI ID:913548

Walter, W R; Mayeda, K; Malagnini, L; Scognamiglio, L

We develop a new methodology to determine apparent attenuation for the regional seismic phases Pn, Pg, Sn, and Lg using coda-derived source spectra. The local-to-regional coda methodology (Mayeda, 1993; Mayeda and Walter, 1996; Mayeda et al., 2003) is a very stable way to obtain source spectra from sparse networks using as few as one station, even if direct waves are clipped. We develop a two-step process to isolate the frequency-dependent Q. First, we correct the observed direct wave amplitudes for an assumed geometrical spreading. Next, an apparent Q, combining path and site attenuation, is determined from the difference between the spreading-corrected amplitude and the independently determined source spectra derived from the coda methodology. We apply the technique to 50 earthquakes with magnitudes greater than 4.0 in central Italy as recorded by MEDNET broadband stations around the Mediterranean at local-to-regional distances. This is an ideal test region due to its high attenuation, complex propagation, and availability of many moderate sized earthquakes. We find that a power law attenuation of the form Q(f) = Q{sub 0}f{sup Y} fit all the phases quite well over the 0.5 to 8 Hz band. At most stations, the measured apparent Q values are quite repeatable from event to event. Finding the attenuation function in this manner guarantees a close match between inferred source spectra from direct waves and coda techniques. This is important if coda and direct wave amplitudes are to produce consistent seismic results.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 913548
• Report Number(s): UCRL-JRNL-227999
• Journal Information: Geophysical Research Letters, Journal Name: Geophysical Research Letters Vol. 34; ISSN GPRLAJ; ISSN 0094-8276
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
AMPLITUDES
ATTENUATION
AVAILABILITY
EARTHQUAKES
ITALY
SPECTRA