SKS splitting beneath the MAGIC FlexArray experiment

Abstract:

The Mid-Atlantic Geophysical Integrative Collaboration (MAGIC) is an EarthScope and GeoPRISMS-funded project that involves a collaborative effort among seismologists, geodynamicists, and geomorphologists to understand the relationships among surface processes, crustal and lithospheric structure, and deep mantle flow beneath eastern North America. The eastern passive continental margin has been modified by multiple episodes of orogenesis and rifting through several cycles of supercontinent assembly and breakup over the past 1.3 billion years of Earth history. The MAGIC Flexible Array broadband seismic deployment began in October 2013, with the main phase of the deployment taking place in October 2014. As of summer 2015 the experiment had 27 stations running; the deployment will demobilize in October 2016. We have investigated splitting of SKS phases measured at MAGIC stations during the early stages of the deployment. As illustrated by this presentation, stations located in the Appalachian Mountains, present fast splitting directions parallel to the strike of the Appalachian range, with delay times of approximately 1 sec. At stations to the east and west of the high topography, we find more complicated splitting patterns, with fast directions that vary over short length scales and a large number of null SKS arrivals over a range of backazimuths. These observations suggest a significant contribution to SKS splitting from anisotropy in the lithospheric upper mantle in our study region.