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<div style=""><span style="font-size: 14pt;"></span><span style="font-size: 14pt;"><b>The Tale of Two Faults: The Young and Loud Versus the Old and Quiet</b></span><br>
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<div style=""><span style="font-size: 12pt;"><b></b></span><span style="font-size: 11pt;"><b></b></span><span style="font-size: 12pt;"><b>Speaker:
</b>Pieter Share</span><span style="font-size: 12pt;"><b><br>
</b></span></div>
<div style=""><span style="font-size: 12pt;"> Oregon State University</span></div>
<div style=""><span style="font-size: 12pt;"><b>Location:</b> online/virtual only</span></div>
<div style=""><span style="font-size: 12pt;"><b>Date/Time: </b>Tuesday, Oct 18, 2022 10-11am MDT</span></div>
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</span></div>
<div style=""><span style="font-size: 12pt;"><span class="ContentPasted0"><b>Abstract: </b></span><span class="ContentPasted0" style="font-size: 12pt;">In southernmost California, only ~40 km separates the near-parallel San Jacinto fault zone (SJFZ) </span></span><span style="font-size: 12pt;">and
Southern San Andreas fault (SSAF) but there is much greater separation from a structural and</span><span style="font-size: 12pt;">
</span><span style="font-size: 12pt;">seismotectonic perspective. The SJFZ transects mostly rocks of the Peninsular Ranges batholith,</span><span style="font-size: 12pt;">
</span><span style="font-size: 12pt;">has an accumulated offset of ~25 km and accommodates abundant and distributed seismicity. In</span><span style="font-size: 12pt;">
</span><span style="font-size: 12pt;">contrast, the SSAF is relatively aseismic on an everyday scale, exhibits frequent shallow creep,</span><span style="font-size: 12pt;">
</span><span style="font-size: 12pt;">has an accumulated offset of 100s of km and now juxtapose crustal blocks of the Peninsular Ranges</span><span style="font-size: 12pt;">
</span><span style="font-size: 12pt;">(southwest) and San Bernardino Mountains (northeast). Both the SJFZ and SSAF have</span><span style="font-size: 12pt;">
</span><span style="font-size: 12pt;">accommodated numerous moderate to large earthquakes and will do so again in future.</span><span style="font-size: 12pt;"><span class="ContentPasted0">
<div class="ContentPasted0" style=""><br>
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<div class="ContentPasted0" style=""><span style="font-size: 12pt;">In this presentation, I will present the diverse passive geophysical toolkit myself and collaborators use to inform the internal features of the SJFZ and SSAF and relate these to past tectonic
activity and their potential effects on the physics of future large earthquake ruptures. In the case of the SJFZ, we detect fault zone head wave (FZHW) signals generated by the distributed seismicity clouds and use these FZHWs to pinpoint a >70 km-long bimaterial
spine (interface) within the</span></div>
<div class="ContentPasted0" style=""><span style="font-size: 12pt;">complex SJFZ that varies in dip, strike and across-fault P- and S-wave velocity contrasts. Along the SSAF, we use a combination of magnetotellurics (MT), large-N seismic array data and analysis
of geodetic signals from shallow creeping events to show that the SSAF likely has a steep northeast dip in the upper crust (at least) over 10s of km along-strike and that strain may be accumulating in more than one location in the ductile crust beneath this
fault. These characteristics have important implications for earthquake rupture speed, mode, directivity and subsequent ground shaking along the SJFZ and SSAF as well as other major transform faults around the world.</span></div>
<div class="ContentPasted0" style=""><br>
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<div class="ContentPasted0" style=""><span class="ContentPasted1"><b>Bio: </b>Dr. Pieter-Ewald Share is an assistant professor in Geophysics at Oregon State University. His group there focusses on the state of structure and strain along active plate margins
in western North America. Dr. Share’s career started with a Bachelors in Geology and Physics in his native South Africa. From there he completed a Masters in Geophysics at the Dublin Institute for Advanced Studies. After moving to the United States in 2013,
he started a PhD at USC in Los Angeles followed by a postdoc at Scripps/IGPP as a Green Fellow. The Share group at OSU is a big proponent of integrative studies in the Geosciences and continues to combine old and new methods to achieve a more holistic understanding
of Earth processes.</span></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>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<span style="font-size:12pt"><b><br>
</b></span></div>
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