Intrinsic and scattering attenuation from observed seismic codas in the Almeria Basin (southeastern Iberian Peninsula)

Abstract

S U M M A R YThe anelastic attenuation in the Almeria Basin (southeastern Iberian Peninsula) is investigated by using seismic data collected during the summer of 1991. A multiple-lapse time-window analysis is applied to high-frequency seismograms corresponding to 20 shallow seismic events with low magnitudes ( m 12.5) and distances less than 71 km, recorded at six short-period seismographic stations. We have constructed corrected geometrical spreading and normalized energy-distance curves for the region over the frequency bands 1-2,2-4,4-8,8-14 and 14-20 Hz. A theoretical model for body-wave energy propagation in a randomly heterogeneous medium has been employed to interpret the observations. Two parameters describe the medium in this model: the scattering attenuation coefficient qs = kQ3 ' and the intrinsic attenuation coefficient yI = kQ, ', where k is the wavenumber and Qr1 and Q, are the intrinsic and scattering attenuation respectively. This model assumes that scattering is isotropic, including all orders of multiple scattering, and predicting the spatial and temporal energy distribution of seismic energy. A least-squares fitting procedure has been used to find the best estimates of the model parameters. The analysis of the spectral amplitude decay of coda waves has provided coda Q,' values at the same frequency bands. The results obtained show that Q, ', Q2 ' and Q, ' decrease with increasing frequency; for frequencies lower than 3 Hz scattering attenuation is stronger than intrinsic absorption and coda Q, ' takes values between intrinsic and total attenuation, being very close to Qy'. Q;' is more frequency-dependent than Q, ; for frequencies greater than 3 Hz intrinsic absorption is the dominant attenuation effect and Q, and Q3 have significant frequency dependence. In order to correlate the results obtained with the major geological and tectonic features of the region, a geotectonic framework for the area is provided and the predominant frequency decay in coda waves is analysed in order to obtain the coda Q frequency dependence following a power law Qc = Qo( f/fo)", where fo is a reference frequency. In this way we have obtained regionalized values of coda Q at 1 Hz (Qo). Finally, a first-order approach has allowed us to obtain intrinsic and scattering quality factors from the obtained QO and v values, leading us to obtain tentative distributions of Q,, Qs and QO at 1 Hz for the area. The derived intrinsic and scattering quality-factor distributions are in good agreement with the tectonic history and the main geological features of the region. Large scattering and intrinsic attenuation (Qs N 80, QI -100) are found in the sedimentary Neogene and Quaternary basin, while scattering is the dominant effect in the old Palaeozoic rocks of the mountains (Qs -200, QI -1000).Intrinsic Q shows a higher sensitivity to the geological characteristics than scattering Q.

A Study of Source Parameters, Site Amplification Functions and Average Effective Shear Wave Quality Factor Qseff from Analysis of Accelerograms of the 1999 Chamoli Earthquake, Himalaya

“…This may reflect the difference in the character of the regions studied. PUJADES et al (1997) have shown that a high intrinsic attenuation quality factor can be found in the regions where low coda-Q b values are estimated. The average Q seff value for the outer Himalaya obtained from the analysis of the 1986 Dharmsala earthquake in the Himachal sector is 240 for an epicentral distance range of 6-25 km .…”

Multiple Lapse Time Window Analysis of the Korean Peninsula Considering Focal Depth

“…The DSMC models are labeled with source depths (0, 5, 10, 15, and 20) Model Freq (Hz) (Mayeda et al, 1992), Kagoshima, Chubu, Shikoku, Japan (Hoshiba, 1993), and the Canary Island (Canas et al, 1998). Dashed lines represent South Apennines (Bianco et al, 2002), Furiuri, Italia (Bianco et al, 2005), Southern Spain (Akinci et al, 1995), and Almeria, Southeastern Spain (Pujades et al, 1997). For the previous study in Korean Peninsula is Southeastern Korea (Chung & Yoshimoto, 2013), and Korea (Chung et al, 2010) (Fig.…”

Intrinsic and Scattering Seismic Attenuation in Southwestern Anatolia

“…Several studies showed that a correct velocity structure instead of a uniform half-space model should serve to better define the attenuation characteristics under the study area of consideration (e.g., see MAYEDA et al, 1992;HOSHIBA 1993;AKINCI et al, 1995;HOSHIBA, 1997;PUJADES et al, 1997;MARGERIN et al, 1999;AKINCI and EYIDOG AN, 2000;HOSHIBA et al, 2001;UGALDE et al, 2002;BIANCO et al, 2002 and2005). Therefore, the present results are only reasonably correct under the simplifying assumptions outlined above.…”