Broadband waveform inversion of ground velocities in the 0.02 0.10 Hz frequency band is successfully applied to 181 earthquakes with ML ≥ 3 of the April, 2009, L'Aquila, Italy, earthquake sequence. This was made possible by the development of a new regional crustal velocity model constrained by deep crustal profiles, surfacewave dispersion and teleseismic Pwave receiver functions and tested through waveform fit. Although all earthquakes exhibit normal faulting, with the fault plane dipping southwest at about 55º for the majority of events, a subset of events had much shallower dips. The issue of confidence in the derived parameters was investigated by applying the same inversion procedure by two groups who subjectively selected different traces for inversion. The unexpected difficulty in modeling the regional broadband waveforms of the mainshock as a point source was investigated through an extensive finitefault modeling of broadband velocity and accelerometer data, which placed the location of major moment release updip and about 47 seconds after the initial firstarrival hypocentral parameters.

[1] The use of local and regional S-wave coda is shown to provide stable amplitude ratios that better constrains source differences between event pairs. We first compared amplitude ratio performance between local and nearregional S and coda waves in the San Francisco Bay region for moderate-sized events, then applied the coda spectral ratio method to the 1999 Hector Mine mainshock and its larger aftershocks. We find (1) average amplitude ratio standard deviations using coda are $0.05 to 0.12, roughly a factor of 3 smaller than direct S-waves for 0.2 < f < 15.0 Hz; (2) coda spectral ratios for the M w 7.0 Hector Mine earthquake and its aftershocks show a clear departure from self-similarity, consistent with other studies using the same datasets; and (3) event-pairs (Green's function and target events) can be separated by $25 km for coda amplitudes without any appreciable degradation, in sharp contrast to direct waves. Citation: Mayeda, K., L. Malagnini, and W. R. Walter (2007), A new spectral ratio method using narrow band coda envelopes: Evidence for non-self-similarity in the Hector Mine sequence, Geophys.

Since 2005, the Italian Civil Protection (Dipartimento della Protezione Cilvile, DPC) has funded several projects driven toward fast assessment of ground motion shaking in Italy-the final goal being that of organizing the emergency and direct the search and rescue (SAR) teams. To this end, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) has started to determine shakemaps using the USGS-ShakeMap package within 30 minutes from event occurrence and adopting a manually revised location. In this paper we present the INGV implementation of USGS-ShakeMap for earthquakes occurring in Italy and immediately neighboring areas. Emphasis is put on data acquisition, the adopted ground motion predictive relations and the site corrections for the local amplifications of the ground motion. Finally, two examples of shakemaps are shown-the first determined for a recent medium size earthquake, the other for the large Irpinia, 1980, M6.9 event. For both events, the maps are compared to the available macroseismic data.

Regressions over a data set of broadband seismograms are performed to quantify the attenuation of the ground motion in the Apennines (Italy), in the 0.25-5.0 Hz frequency band. The data set used in this article consists of over 6000 horizontal-component seismograms from 446 events, with magnitude ranging from M w Ӎ 2 to M w ‫ס‬ 6.0. Waveforms were collected during recent field experiments along the Apennines. Data from two MedNet broadband stations, located in central and southern Apennines, were also used. Seismograms are bandpass-filtered around a set of sampling frequencies, and the logarithms of their peak values are written as AMP(f, r) ‫ס‬ EXC(f, r) ‫ם‬ SITE(f) ‫ם‬ D(r, r , f). ref ref EXC(f , r ref) is the excitation term for the ground motion at the hypocentral distance r ref. SITE(f) represents the distortion of the seismic spectra induced by the shallow geology at the recording site. D(r, r ref , f) includes the effects of the geometrical spreading, g(r), and of a frequency-dependent crustal attenuation Q. It is determined as a piecewise linear function, allowing to consider complex behavior of the regional attenuation. A first estimate of D(r, r ref , f) is obtained using a coda normalization technique (Aki, 1980; Frankel et al., 1990) and used as a starting model in the inversion of the peak values. Then, by trial and error, the empirical D(r, r ref , f) is fitted using a trilinear geometrical spreading, with crossover distances at 30 and 80 km, and the crustal parameter 0.10 f Q(f) ‫ס‬ 130 ; f ‫ס‬ 1.0 Hz ref f ref These results suggest a low-Q crust in the entire Apennines in the 0.25-5.0 Hz range, implying that the seismic hazard in the region may be dominated by the local seismicity. The final section is devoted to highlight the limitations of the formula proposed by Console et al. (1988) to estimate duration magnitudes M d in Italy.

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