Towards and Understanding of the Stability of Lg Amplitudes

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

Using repeated Reverse Two Station (RTS) measurements we have been able to quantify the stability and reliability of high-frequency Lg attenuation. We have noticed that for many regions Lg amplitudes can be quite unstable leading to large uncertainties in estimates of Lg Q(f). Since the reverse two station paths should effectively eliminate source and site effects, the path effects should be consistent for all repeated paths. Therefore, we are only left a number of the possible explanations for the observed large variations in the RTS amplitude reductions. In this study, we use an approach that we term the Double Two Station Method (DTSM) to measure the effect of the source depth and the source epicentral distance to Lg Q.

In this work, we have examined the behavior of the DQV (the difference of the Lg Q value multiplied by the Lg velocity) for a large number of DTSM station paths in the northern Middle East. We observe a distinct decrease in the stability of Q value as the distance between the two events increases for some station pairs in the northern Zagros Mountains. Different path lengths could likely lead to different modes of Lg propagation, which sample different parts of the crust and thus give different observed Q values. There is still overlap in the distribution of the DQV values for events located close by and those farther apart. This would suggest that there are still other significant causes for high-frequency Lg amplitude instability. One possible explanation is that the source depth could lead to significant variations in Q values. We are using a similar approach to isolate the effect of source depth on the variations in Lg propagation.

Presenting Author: Duyi Li

Authors