A massive earthquake swarm driven by magmatic intrusion at the Bransfield Strait, Antarctica
Authors: Cesca Simone , Sugan Monica , Rudzinski Łukasz , Vajedian Sanaz , Niemz Peter , Plank Simon , Petersen Gesa , Deng Zhiguo , Rivalta Eleonora , Vuan Alessandro , Plasencia Linares Milton Percy , Heimann Sebastian , Dahm Torsten 
Published: March 2022

&lt;p&gt;&lt;span&gt;A swarm &lt;/span&gt;&lt;span&gt;of&lt;/span&gt; &lt;span&gt;~8&lt;/span&gt;&lt;span&gt;5&lt;/span&gt;&lt;span&gt;,000 &lt;/span&gt;&lt;span&gt;volcano-tectonic earthquakes started in August 2020 &lt;/span&gt;&lt;span&gt;at&lt;/span&gt;&lt;span&gt; the Bransfield Strait, &lt;/span&gt;&lt;span&gt;between &lt;/span&gt;&lt;span&gt;the&lt;/span&gt;&lt;span&gt; South Shetland Islands and the Antar&lt;/span&gt;&lt;span&gt;c&lt;/span&gt;&lt;span&gt;tic Peninsula. &lt;/span&gt;&lt;span&gt;The Bransfield Basin is a unique &lt;/span&gt;&lt;span&gt;back-arc basin, &lt;/span&gt;&lt;span&gt;where t&lt;/span&gt;&lt;span&gt;he past a&lt;/span&gt;&lt;span&gt;ctive subduction slowed &lt;/span&gt;&lt;span&gt;down &lt;/span&gt;&lt;span&gt;dramatically &lt;/span&gt;&lt;span&gt;~&lt;/span&gt;&lt;span&gt;4 Ma, leaving a small remnant of the former Phoenix plate incorporated in the Antarctic plate. &lt;/span&gt;&lt;span&gt;Today t&lt;/span&gt;&lt;span&gt;here is no clear evidence for &lt;/span&gt;&lt;span&gt;recent &lt;/span&gt;&lt;span&gt;normal seafloor spreading.&lt;/span&gt;&lt;span&gt; Continental crust is thinning to develop oceanic crust and the current extension is either attributed to the Phoenix Block subduction and rollback or to shear between the Scotia and Antarctic plates. &lt;/span&gt; &lt;span&gt;The &lt;/span&gt;&lt;span&gt;2020 &lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;eismicity occur&lt;/span&gt;&lt;span&gt;red&lt;/span&gt; &lt;span&gt;close to the Orca submarine volcano, &lt;/span&gt;&lt;span&gt;previously &lt;/span&gt;&lt;span&gt;considered inactive. &lt;/span&gt;&lt;span&gt;G&lt;/span&gt;&lt;span&gt;eodetic data re&lt;/span&gt;&lt;span&gt;ported&lt;/span&gt; &lt;span&gt;a transient deformation with &lt;/span&gt;&lt;span&gt;up to &lt;/span&gt;&lt;span&gt;~&lt;/span&gt;&lt;span&gt;11&lt;/span&gt;&lt;span&gt; cm&lt;/span&gt; &lt;span&gt;northwestward displacement&lt;/span&gt;&lt;span&gt; over King George Island&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;We use a &lt;/span&gt;&lt;span&gt;wide&lt;/span&gt; &lt;span&gt;variety of geophysical &lt;/span&gt;&lt;span&gt;data and &lt;/span&gt;&lt;span&gt;methods to &lt;/span&gt;&lt;span&gt;re&lt;/span&gt;&lt;span&gt;veal&lt;/span&gt; &lt;span&gt;the&lt;/span&gt;&lt;span&gt; complex migration &lt;/span&gt;&lt;span&gt;of seismicity&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;accompanying the intrusion of &lt;/span&gt;&lt;span&gt;0.26-0.56&lt;/span&gt; &lt;span&gt;k&lt;/span&gt;&lt;span&gt;m&lt;/span&gt;&lt;sup&gt;&lt;span&gt;3&lt;/span&gt;&lt;/sup&gt;&lt;span&gt;of &lt;/span&gt;&lt;span&gt;magma &lt;/span&gt;&lt;span&gt;off the Orca seamount&lt;/span&gt;&lt;span&gt; at ~&lt;/span&gt;&lt;span&gt;20&lt;/span&gt;&lt;span&gt; km depth&lt;/span&gt;&lt;span&gt;.&lt;/span&gt; &lt;span&gt;D&lt;/span&gt;&lt;span&gt;eeper, &lt;/span&gt;&lt;span&gt;clustered&lt;/span&gt;&lt;span&gt; strike-slip earthquakes &lt;/span&gt;&lt;span&gt;mark the&lt;/span&gt;&lt;span&gt; magmatic intrusion &lt;/span&gt;&lt;span&gt;at &lt;/span&gt;&lt;span&gt;depth&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;while&lt;/span&gt;&lt;span&gt; shallower normal faulting &lt;/span&gt;&lt;span&gt;events&lt;/span&gt; &lt;span&gt;are &lt;/span&gt;&lt;span&gt;induced&lt;/span&gt;&lt;span&gt; by&lt;/span&gt; &lt;span&gt;the&lt;/span&gt; &lt;span&gt;growth of a lateral dike, extending &lt;/span&gt;&lt;span&gt;~&lt;/span&gt;&lt;span&gt;2&lt;/span&gt;&lt;span&gt;0&lt;/span&gt;&lt;span&gt; km &lt;/span&gt;&lt;span&gt;NE-SW&lt;/span&gt;&lt;span&gt;.&lt;/span&gt; &lt;span&gt;Seismicity abruptly decreased after the largest M&lt;/span&gt;&lt;span&gt;w&lt;/span&gt;&lt;span&gt; 6.0 earthquake, suggesting the &lt;/span&gt;&lt;span&gt;magmatic &lt;/span&gt;&lt;span&gt;dike lost pressure &lt;/span&gt;&lt;span&gt;with&lt;/span&gt;&lt;span&gt; the &lt;/span&gt;&lt;span&gt;slipping of a large fault and&lt;/span&gt; &lt;span&gt;the &lt;/span&gt;&lt;span&gt;opening of upward paths. &lt;/span&gt;&lt;span&gt;A&lt;/span&gt;&lt;span&gt; seafloor eruption &lt;/span&gt;&lt;span&gt;is likely&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;but not&lt;/span&gt;&lt;span&gt; confirm&lt;/span&gt;&lt;span&gt;ed&lt;/span&gt;&lt;span&gt; by sea surface &lt;/span&gt;&lt;span&gt;roughness &lt;/span&gt;&lt;span&gt;or temperature &lt;/span&gt;&lt;span&gt;anomalies&lt;/span&gt;&lt;span&gt;. The unrest &lt;/span&gt;&lt;span&gt;documents episodic magmatic intrusion &lt;/span&gt;&lt;span&gt;in the Bransfield Strait &lt;/span&gt;&lt;span&gt;and provides unique insights into&lt;/span&gt; &lt;span&gt;active&lt;/span&gt;&lt;span&gt; continental rifting&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;