Attenuation of 1–6 s L_g waves in Eurasia

Abstract

We report our investigation of the Lg attenuation characteristics in Eurasia using digital recordings from the Incorporated Research Institutions for Seismology/Chinese Digital Seismic Network broadband stations. To maximize the utilization of the current station and source distribution in the region, we have derived a new technique known as the source pair/receiver pair (SPRP) method for Lg attenuation measurement. The procedure eliminates seismic source and site effects, leaving behind decontaminated amplitude data from which regional wave attenuation is estimated. For Lg attenuation studies the SPRP method is more flexible and of greater general applicability than its predecessor, the reversed two‐station method (Chun et al., 1987). The application of the SPRP method to our time domain analysis of 33 regional and far‐regional seismic events has provided stable regional average for Lg attenuation in periods of 1–6 s. Our time domain analysis, aided by a damped least squares inversion algorithm, has led to robust measurements of Lg attenuation (Q) and its frequency dependence (η) in nine subregions of tectonic significance. Regions of active tectonics and seismicity generally have lower Q0 than that in the stable continental interior. Subregional Q and η are found compatible with the published results in areas of relatively uniform geology; η values are comparatively poorly determined, suggesting that they are susceptible to the presence of crustal heterogeneities along the wave paths.

Characteristics of Lg attenuation in the Tibetan Plateau

“…For eastern Tibet, where sufficient Lg signal‐to‐noise ratios were observed, a frequency‐dependent Q Lg function given by Q Lg ( f ) = (366 ± 37) f (0.45±0.06) was estimated for the passband (0.5–16 Hz) [ McNamara et al , 1996]. This is comparable to the estimate of Q Lg ( f ) = (448 ± 82) f (0.426±0.157) estimated for 1–6 s Lg waves traversing Tibet by Shih et al [1994]. This latter value is likely also dominated by eastern Tibet paths, as “blocked” observations were omitted from the calculation.…”

“…We also could not detect any systematic variation with source focal mechanism for the events with Harvard CMT solutions, although such dependence may be rather complex. Lg radiation patterns are often treated as isotropic for gross measurements such as ours [e.g., Shih et al , 1994], and we will make this assumption below.…”

A Study of the Regional Variation of Low-Frequency around the Korean Peninsula

“…The reversed two station method (RTSM) (Chun et al, 1987) gave anomalously high Q 1 Lg (Chung, 2002;Chung and Lee, 2002) due to short interstation paths (< 130 km) for South Korean stations. Relaxing the collinear restriction on the sources and receivers (Shih et al, 1994), the extended interstation paths (< 505 km) gave a lower Q 1 Lg (< 0:002) for 1-3 Hz in South Korea (Chung et al, 2005), typical low values for tectonically inactive regions. This earlier study, however, neglected regional variations such as potential high Q 1 Lg in the coastal region of the Sea of Japan (East Sea).…”

Regional Attenuation in Northern California: A Comparison of Five 1D Q Methods

“…The SPRP method is implemented in the frequency domain by Fan and Lay (2003b) and in the time domain by Shih et al (1994) and Chung et al (2005) where they find clusters in small regions that are very different from the overall 1-D Q model. The SPRP method in the time domain is much better suited for a large homogeneous region, where several interstation regions can be grouped together.…”

“…The SPRP method is the RTS method with a relaxation on the narrow azimuthal window requirement (Shih et al, 1994). We implement this method in the time domain so that equation (11) becomes…”