Eric M. Matzel

Joint inversion for three-dimensional S velocity mantle structure along the Tethyan margin

Abstract : For purposes of studying the lateral heterogeneity as well as for ultimately predicting seismograms for this region, we construct a new 3-D S-velocity model by jointly inverting a variety of different seismic data. We jointly invert regional waveforms, surface wave group velocity measurements, teleseismic S arrival times, and crustal thickness estimates from receiver functions, refraction lines, and gravity surveys. These data types have complementary resolving power for crust and mantle structures, vertical and lateral variations, shallow and deep mantle features, local and global structure. Therefore, a joint inversion of these data sets might help unravel the complexity of this tectonically diverse area. These measurements are made from a combination of mantle investigation of the deep suture between Europe and Africa (MIDSEA), Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL), GeoScope, Geofon, Global Seismographic Network (GSN), International Deployment of Accelerometeres (IDA), MedNet, national networks, and local deployments throughout the study region which extends from the western Mediterranean region to the Hindu Kush and encompasses northeastern Africa, the Arabian peninsula, the Middle East, and part of the Atlantic Ocean for reference. We have fitted the waveforms of regional S and Rayleigh waves from over 3800 seismograms using Partitioned Waveform Inversion. We include over 3000 crustal thickness estimates from receiver functions, gravity measurements, and refraction profiles. We include Rayleigh wave group velocities for hundred thousands of paths transecting the region. We have over 3000 teleseismic S arrival times measured through cross correlation and over 170000 from picks originally reported to the International Seismological Centre (ISC).

Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean

In this study, ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along an extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.