Source Parameters for the Community Stress Drop Validation Study
Authors: Kemna Kilian B. , Harrington Rebecca M. 
Published: March 2022

&lt;div&gt;&lt;span&gt;The c&lt;/span&gt;&lt;span&gt;ommunity&lt;/span&gt;&lt;span&gt;-led&lt;/span&gt; &lt;span&gt;s&lt;/span&gt;&lt;span&gt;tress &lt;/span&gt;&lt;span&gt;d&lt;/span&gt;&lt;span&gt;rop &lt;/span&gt;&lt;span&gt;v&lt;/span&gt;&lt;span&gt;alidation &lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;tudy&lt;/span&gt; &lt;span&gt;initiated in early 2021&lt;/span&gt;&lt;span&gt; aims at &lt;/span&gt;&lt;span&gt;understand&lt;/span&gt;&lt;span&gt;ing&lt;/span&gt;&lt;span&gt; and resolv&lt;/span&gt;&lt;span&gt;ing&lt;/span&gt;&lt;span&gt; differences&lt;/span&gt;&lt;span&gt; in stress drop measurements&lt;/span&gt;&lt;span&gt; us&lt;/span&gt;&lt;span&gt;ing&lt;/span&gt;&lt;span&gt; a consistent dataset of the 2019 Ridgecrest &lt;/span&gt;&lt;span&gt;e&lt;/span&gt;&lt;span&gt;arthquake &lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;equenc&lt;/span&gt;&lt;span&gt;e&lt;/span&gt;&lt;span&gt;. The dataset consists of &lt;/span&gt;&lt;span&gt;13,000 earthquakes&lt;/span&gt;&lt;span&gt; with phase arrivals at up to 107 stations in &lt;/span&gt;&lt;span&gt;the&lt;/span&gt;&lt;span&gt; week following the M7.1 mainshock on &lt;/span&gt;&lt;span&gt;2019-07-04.&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/div&gt;&lt;div&gt;&amp;#160;&lt;/div&gt;&lt;div&gt;&lt;span&gt;Stress drop&lt;/span&gt;&lt;span&gt; value&lt;/span&gt;&lt;span&gt;s are commonly estimated by fitting theoretical source models to direct&lt;/span&gt;&lt;span&gt; phase&lt;/span&gt; &lt;span&gt;(P-&lt;/span&gt;&lt;span&gt; or S-wave) or coda wave spectra.&lt;/span&gt;&lt;span&gt; In this work, w&lt;/span&gt;&lt;span&gt;e contribute&lt;/span&gt; &lt;span&gt;to&lt;/span&gt;&lt;span&gt; the community-led study using&lt;/span&gt;&lt;span&gt; different approaches based on earthquake spectra and an &lt;/span&gt;&lt;span&gt;alternative approach &lt;/span&gt;&lt;span&gt;based on stopping phases to &lt;/span&gt;&lt;span&gt;estimate fault dimension and rupture velocity&lt;/span&gt; &lt;span&gt;(the&lt;/span&gt;&lt;span&gt; main parameters modulating stress drop)&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;The Ridgecrest dataset offers a unique opportunity to explore the applicability, potential benefits, and limitations of each method due to a wide range of earthquake magnitudes, &lt;/span&gt;&lt;span&gt;variety&lt;/span&gt;&lt;span&gt; of seismic instruments, and extensive body of&lt;/span&gt;&lt;span&gt; supporting&lt;/span&gt;&lt;span&gt; research &lt;/span&gt;&lt;span&gt;related to the&lt;/span&gt;&lt;span&gt; sequence. Furthermore, the sequence enables the comparison between different methods to &lt;/span&gt;&lt;span&gt;identify&lt;/span&gt; &lt;span&gt;consistencies and differences &lt;/span&gt;&lt;span&gt;between&lt;/span&gt;&lt;span&gt; estimates using&lt;/span&gt;&lt;span&gt; different methodologies.&amp;#160;&lt;/span&gt;&lt;/div&gt;&lt;div&gt;&amp;#160;&lt;/div&gt;&lt;div&gt;&lt;span&gt;W&lt;/span&gt;&lt;span&gt;e will&lt;/span&gt;&lt;span&gt; present&lt;/span&gt;&lt;span&gt; stress drop&lt;/span&gt;&lt;span&gt; estimate&lt;/span&gt;&lt;span&gt;s using&lt;/span&gt;&lt;span&gt; commonly used&lt;/span&gt;&lt;span&gt; frequency-based&lt;/span&gt; &lt;span&gt;methods&lt;/span&gt;&lt;span&gt;,&lt;/span&gt; &lt;span&gt;such as&lt;/span&gt;&lt;span&gt; single&lt;/span&gt;&lt;span&gt;-&lt;/span&gt;&lt;span&gt;spectr&lt;/span&gt;&lt;span&gt;um&lt;/span&gt;&lt;span&gt; and spectral&lt;/span&gt;&lt;span&gt;-&lt;/span&gt;&lt;span&gt;ratio fitting. &lt;/span&gt;&lt;span&gt;We also further examine the &lt;/span&gt;&lt;span&gt;validity of the theoretical assumptions made for each method&lt;/span&gt;&lt;span&gt; using an&lt;/span&gt;&lt;span&gt;stopping&lt;/span&gt;&lt;span&gt;-&lt;/span&gt;&lt;span&gt;phase&lt;/span&gt;&lt;span&gt; based estimates of rupture velocity&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;span&gt; &amp;#160;&lt;/span&gt;&lt;span&gt;First results show &lt;/span&gt;&lt;span&gt;clear detections of&lt;/span&gt;&lt;span&gt; stopping phases for &lt;/span&gt;&lt;span&gt;a subset &lt;/span&gt;&lt;span&gt;of earthquakes&lt;/span&gt;&lt;span&gt; that imply &lt;/span&gt;&lt;span&gt;stress drop &lt;/span&gt;&lt;span&gt;values ranging&lt;/span&gt;&lt;span&gt; between 0.1 - 10 MPa. The range agrees with the results from the frequency-based methods, and estimates from different methods show similar patterns. &lt;/span&gt;&lt;span&gt;The first results also suggest significant &lt;/span&gt;&lt;span&gt;deviat&lt;/span&gt;&lt;span&gt;ion of specific individual earthquake estimates, which will also be explored by a detailed comparison of methods&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/div&gt;