Along-Arc and Back-Arc Attenuation, Site Response, and Source Spectrum for the Intermediate-Depth 8 January 2006 M 6.7 Kythera, Greece, Earthquake

Abstract

An M 6.7 intermediate-depth (66 km), in-slab earthquake occurring near the island of Kythera in Greece on 8 January 2006 was well recorded on networks of stations equipped with acceleration sensors and with broadband velocity sensors. All data were recorded digitally using recording instruments with resolutions ranging from almost 11 to 24 bits. We use data from these networks to study the distance dependence of the horizontal-component Fourier acceleration spectra (FAS) and horizontal-component pseudoabsolute response spectral acceleration (PSA). For purposes of simulating motions in the future, we parameterize the distance decay using several forms of the geometrical-spreading function, for each of which we derive Q as a function of frequency. By extrapolating the distance decay back to 1 km, we obtain a reference spectrum that can be used in future simulations. This spectrum requires a more complicated spectral shape than the classic single-corner-frequency model; in particular, there appears to be an enhancement of motion around 0.2-0.3 Hz that may be due to the radiation of a 3-5 sec pulse from the source. We infer a κ 0 value of about 0.055 sec for rock stations and a stress parameter in the range of 400-600 bars. We also find distinctive differences in the site response of stations on soft soil and soil; both the FAS and the 5% damped PSA amplifications have similar peak amplitudes (about 2 and 4 for soil and soft-soil sites, respectively, relative to the rock sites) at similar frequencies (between about 0.4 and 2.0 Hz, with the soft-soil amplifications peaking at somewhat lower frequencies than the soil amplifications). One of the most distinctive features of the data is the clear difference in the motions for along-arc and back-arc stations, with the former being significantly higher than the latter over a broad range of frequencies at distances beyond about 250 km. The motions from the Kythera earthquake are roughly comparable to those from intermediate-depth earthquakes elsewhere, but they appear to be significantly higher than those from recordings of shallow earthquakes in Greece of comparable magnitude and hypocentral distance. Name Date Origin Time Epicenter: Latitude Epicenter: Longitude Depth M

Geo-Characterization at selected accelerometric stations in Crete (Greece) and comparison of earthquake data recordings with EC8 elastic spectra

“…For the recording 19940523_064612_CHN1 (Figure 9(b)), the observed lack of energy for periods greater than about 1sec is probably due to the low resolution of the analog instrument installed (SMA-1, see Table 4). The Heraklion city stations HER1, HER2 and HER3 (Figures 9(a), 9(d), 9(e), 9(g), 9(j), 9(k) and 9(l)) show large deviations in the compared spectral shapes, especially for periods 0.8 sec to 1.8 sec, in agreement with results of previous work [23][24][25]. For recordings 19940523_064612_HER1 (Figure 9(a)) and 20060108_113455_HER2 ( Figure 9(d)), the observed lack of energy for periods greater than about 1 sec is probably due to low resolution analog (SMA-1) and digital SSA-2 (12 bits) instruments (see Table 4).…”

Earthquake vulnerability and seismic risk assessment of urban areas in high seismic regions: application to Chania City, Crete Island, Greece

“…The earthquake's epicenter as estimated by the European Mediterranean Seismological Center (EMSC-CSEM, http://emsc-csem.org) was 36.31°N, 23.24°E, and the focal depth was 60 km. The shock was felt in a spatially extended area that covered Greece, Italy, Turkey, Egypt, Cyprus, Israel, Syria, Jordan and Lebanon (Konstantinou et al , 2009Boore et al 2009;Nikolintaga et al 2008). The recorded PGA (peak ground acceleration) in Chania (93 km, epicentric distance) was 41 mg ).…”

Fore-Arc and Back-Arc Ground Motion Prediction Model for Vrancea Intermediate Depth Seismic Source

“…This wedge filters out the high-frequency content of motions propagating from deep-focus in-slab events that traverse the wedge Kanno et al, 2006;Dhakal et al, 2008;Zhao et al, 2006]. As typical examples for FA/BA attenuation contrast, we can mention: Japan Dhakal et al, 2008;Zhao et al, 2006;Takanami et al, 2000;Nakamura and Uetake, 2000;Yoshimoto et al, 2006;Ghofrani and Atkinson, 2013]; Hellenic Arc [Papazachos and Comninakis, 1971;Spakman et al, 1988;Papazachos and Nolet, 1997;Boore et al, 2009]; Calabrian Arc [Monna and Dahm, 2009]; Mexican 536 R. Vacareanu et al subduction earthquakes [García et al, 2004;Aguirre andIrikura 2007, Chen andClayton, 2009]; Casacadia region [Atkinson and Boore, 2003;Crouse, 1991;Gregor et al, 2002]; Alaska [Stachnik et al, 2004]; New Zealand [McVerry et al, 2006;Eberhart-Phillips et al, 2008]; worldwide, for subduction earthquakes [Abrahamson et al, 2012].…”