Transition Zone Wave Propagation: Characterizing Travel-Time and Amplitude Information
CALIFORNIA UNIV SAN DIEGO LA JOLLA
Pagination or Media Count:
We characterize transition-zone seismic wave propagation by mapping and calibrating the travel-time and amplitude behavior of P waves traveling through the transition zone at epicentral distances from 13 to 30 degrees and modeling the triplications resulting from the 410- and 660-km discontinuities. We have built an online database of waveforms from the IRIS FARM archive, which consists of broadband data from the global seismic networks as well as portable seismic arrays deployed in PASSCAL experiments. We process the data to compute source and station amplitude terms to correct for different magnitude sources and near-receiver site effects as well as errors in the instrument response functions. We then compute both global and regional stacks to obtain the average time and amplitude of the wavefield within the 13- to 30-degree distance interval. Because the timing of the secondary branches is variable, we implement an envelope-function stacking method to obtain robust results. We model our data stacks using WKBJ synthetic seismograms and a niching genetic algorithm to explore the model space of different transition-zone velocity structures. We compare these results with long-wavelength models of410- and 660-km discontinuity topography obtained from 55 precursors and more detailed images beneath individual seismic stations derived from receiver functions. Our goal is to produce integrated transition-zone models of seismic velocity and discontinuity topography that will improve our ability to locate and estimate magnitudes of events recorded at regional distances.
- Nuclear Explosions and Devices (Non-Military)