A decade of short-period earthquake rupture histories from multi-array back-projection
Authors: Vera Felipe , Tilmann Frederik , Saul Joachim 
Published: March 2022

&lt;p&gt;&lt;span&gt;Teleseismic&lt;/span&gt;&lt;span&gt; back-projection has emerged as a widely-used tool for understanding the rupture histories of large earthquakes. However, its application often suffers from artifacts related to the receiver array geometry, notably the `swimming' artifact. We present a &lt;/span&gt;&lt;span&gt;teleseismic&lt;/span&gt;&lt;span&gt; back-projection method with multiple arrays and combined P and &lt;/span&gt;&lt;span&gt;pP&lt;/span&gt;&lt;span&gt; waveforms. The method is suitable for defining arrays ad-hoc in order to achieve a good azimuthal distribution for most earthquakes&lt;/span&gt;.&lt;/p&gt;&lt;p&gt;&lt;span&gt;We present a catalog of&lt;/span&gt; &lt;span&gt;short-period&lt;/span&gt; &lt;span&gt;rupture histories (0.5-2.0 Hz) &lt;/span&gt;&lt;span&gt;containing &lt;/span&gt;&lt;span&gt; 54 &lt;/span&gt;&lt;span&gt;events &lt;/span&gt;&lt;span&gt;from 2010 to 2021 &lt;/span&gt;&lt;span&gt;(&lt;/span&gt;&lt;span&gt;M&lt;/span&gt;&lt;span&gt;w&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&amp;#8805;&lt;span&gt; 7.5&lt;/span&gt;&lt;span&gt;)&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;including &lt;/span&gt;&lt;span&gt;recent &lt;/span&gt;&lt;span&gt;and significant&lt;/span&gt; &lt;span&gt;earthquake ruptures&lt;/span&gt;&lt;span&gt;,&lt;/span&gt;&lt;span&gt; e.g., 2021 &lt;/span&gt;&lt;span&gt;Mw 8.3 &lt;/span&gt;&lt;span&gt;South of Sandwich Islands, 2021 &lt;/span&gt;&lt;span&gt;Mw 8.2 &lt;/span&gt;&lt;span&gt;Chignik, 2021 &lt;/span&gt;&lt;span&gt;Mw 8.1 &lt;/span&gt;&lt;span&gt;Kermadec Islands, &lt;/span&gt;&lt;span&gt;and 2020 &lt;/span&gt;&lt;span&gt;Mw 7.8 &lt;/span&gt;&lt;span&gt;Simeonof Island&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The method provides semi-automatic estimates of rupture length, directivity, speed, and aspect ratio, which are related to the complexity of large ruptures. We determined short-period rupture length scaling relations that are in good agreement with previously published relations based on estimates of total slip. Rupture speeds were consistently in the sub-Rayleigh regime for thrust and normal earthquakes, whereas strike-slip events propagated in the unstable &lt;/span&gt;&lt;span&gt;supershear&lt;/span&gt;&lt;span&gt; range. Many of the rupture histories exhibited complex behaviors such as rupture on conjugate faults &lt;/span&gt;&lt;span&gt;(e.g., &lt;/span&gt;&lt;span&gt;2018 Mw 7.9 Gulf of Alaska&lt;/span&gt;&lt;span&gt;)&lt;/span&gt;&lt;span&gt;, bilateral ruptures &lt;/span&gt;&lt;span&gt;(e.g., 2017 Mw 7.8 Komandorsky Islands)&lt;/span&gt;&lt;span&gt;, and dynamic triggering by a P wave &lt;/span&gt;&lt;span&gt;(e.g., 2016 Mw 7.9 Solomon Islands)&lt;/span&gt;&lt;span&gt;. For &lt;/span&gt;&lt;span&gt;megathrust&lt;/span&gt;&lt;span&gt; earthquakes, ruptures encircling asperities were frequently observed, with down-dip &lt;/span&gt;&lt;span&gt;(e.g., 2021 &lt;/span&gt;&lt;span&gt;Mw 8.1 &lt;/span&gt;&lt;span&gt;Kermadec Islands)&lt;/span&gt;&lt;span&gt;, up-dip &lt;/span&gt;&lt;span&gt;(e.g., 2016 Mw 7.8 Pedernales)&lt;/span&gt;&lt;span&gt;, double encircling &lt;/span&gt;&lt;span&gt;(e.g., 2015 Mw 8.3 Illapel)&lt;/span&gt;&lt;span&gt;, and segmented &lt;/span&gt;&lt;span&gt;(e.g., 2020 Mw 7.8 Simeonof Island) &lt;/span&gt;&lt;span&gt;patterns. Although there is a preference for short-period emissions to emanate from central and down-dip parts of the &lt;/span&gt;&lt;span&gt;megathrust&lt;/span&gt;&lt;span&gt;, emissions up-dip of the main asperities are more frequent than suggested by earlier results.&lt;/span&gt;&lt;/p&gt;