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<div style="" class="ContentPasted0"><b><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 14pt;">Links between slab dehydration and forearc seismogenic zone structure from magnetotelluric imaging</span><br>
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<div style=""><font color="#201f1e" face="Calibri, sans-serif"><span style="font-size:12pt"><b>Speaker:
</b>Darcy Cordell</span></font></div>
<div style=""><font color="#201f1e" face="Calibri, sans-serif"><span style="font-size:12pt"> University of Alberta</span></font></div>
<div style=""><font color="#201f1e" face="Calibri, sans-serif"><span style="font-size:12pt"><b>Location:</b> online (while the speaker will be virtual, we will still be projecting the talk in the seminar room so come join us!)</span></font></div>
<div style=""><font color="#201f1e" face="Calibri, sans-serif"><span style="font-size:12pt"><b>Date/Time:
</b>April 4, 2023, 10-11AM MDT</span></font></div>
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<div style=""><font color="#201f1e" face="Calibri, sans-serif"><span style="font-size:12pt"><span class="ContentPasted1"><b>Abstract: </b>Fluids in subduction zones influence many important geological processes as the hydrated incoming plate lithosphere (i.e.
slab) releases pore-bound and chemically-bound water into the over-riding crust and mantle wedge. In particular, fluids released from the slab beneath the forearc seismogenic zone are thought to create conditionally-stable regions which have strain-dependent
slip behavior and may control megathrust rupture. The Shumagin Gap is unique along the Aleutian arc for its paucity of historical megathrust (>8 Mw) rupture nucleating in the gap. Geodetic data suggest that gap is weakly-coupled relative to adjacent segments.
The reasons for the weak coupling and lack of megathrust rupture are unclear. Furthermore, the adjacent Semidi segment ruptured in July 2020 with Mw 7.6 and propagated into the Shumagin Gap. To examine the role of fluids, marine magnetotelluric (MT) data were
collected along a 250 km trench-perpendicular profile in 2019 as part of the Electromagnetic Alaskan GeoPRISMS Experiment (EMAGE). The resulting 2-D resistivity model contains a conductor near the plate interface and is correlated with a wide-band of reflectors
from seismic studies, seismicity, and the July 2020 rupture patch. This suggests that fluids play an important role in controlling the slip behavior in the Shumagin Gap. The source of the fluids at the plate interface is commonly thought to come from the downgoing
slab crust. However, the MT results indicate a significant slab mantle conductor >15 km below the slab Moho, directly beneath (and connected to) the conductor at the plate interface. This suggests that deeper slab mantle serpentinization may reach pressure-temperature
conditions conducive to dehydration beneath the forearc seismogenic zone. This provides an additional source of forearc fluids not previously considered in subduction zone water budgets which can modulate slip behaviour.</span></span></font></div>
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<div style=""><font color="#201f1e" face="Calibri, sans-serif"><span style="font-size:12pt"><b>Bio:</b> Darcy Cordell is a post-doc at the University of Alberta working with Ian Mann using magnetotelluric data for space weather hazards prediction. He completed
his PhD in 2020 working with Martyn Unsworth at the University of Alberta imaging volcanoes and subduction zones in central Chile, and completed a post-doc in 2022 at Georgia Tech working with Samer Naif imaging the Alaska subduction zone and incorporating
petrological constraints on MT interpretations. His main research interests focus on using magnetotellurics for a wide array of applications including imaging magmatic systems, imaging subduction zone fluids, and estimating geoelectric fields during space
weather events. He recently returned from field work in Costa Rica trying to image subduction zone fluids beneath the Nicoya Peninsula.</span></font></div>
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<div style=""><font color="#201f1e" face="Calibri, sans-serif"><span style="font-size: 12pt; color: rgb(102, 102, 102);">For questions, comments, or speaker suggestions, please contact the </span></font><b style="color:inherit; font-family:inherit; font-size:12pt; font-style:inherit; font-variant-ligatures:inherit; font-variant-caps:inherit"><span style="font-weight:400"><span style="font-size: 12pt; font-family: Calibri, sans-serif; color: rgb(102, 102, 102);">GHSC
Seminar Committee: Andrea Llenos <allenos@usgs.gov>, Benjamin Murphy <bmurphy@usgs.gov>, Lauren Schaefer <lschaefer@usgs.gov></span></span></b></div>
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