Abstract

We present the results of a study on the propagation of Lg within the Tibetan Plateau. We analyze over 1200 seismograms for Lg propagation from 185 local and regional earthquakes recorded at distances from 150 to 2000 km, 52 of which are located within the Tibetan Plateau. Although the propagation of Lg has been observed across most of Asia, Lg has not been observed for paths crossing the Tibetan Plateau. We analyze paths that cross the plateau boundaries and paths contained entirely within the Tibetan Plateau. Lg is generated within the Tibetan Plateau and can propagate to epicentral distances of at least 600 km. For events located outside of the Tibetan Plateau, Lg is either absent or severely diminished for paths that cross both the Himalayan and Kunlun ranges, confirming that the margins of the plateau weaken Lg transmission.

Based on the observations from our qualitative analysis, we invert Lg amplitudes for event/station paths that are confined to the Tibetan Plateau to estimate the quality factor, Q. The inversion yields a frequency-dependent Q function:

 
Q(f)=(366±37)f(0.45±0.06)(0.5f16Hz).

Similar observations in other areas indicate that frequency-dependent apparent Q within the Tibetan Plateau is well below that expected for a typical continental interior. Instead, it has a frequency dependence that is characteristic of a tectonically active region.

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