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<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>J.L. Hardebeck</dc:contributor>
  <dc:creator>Debi Kilb</dc:creator>
  <dc:date>2006</dc:date>
  <dc:description>&lt;p class="p1"&gt;&lt;span class="s1"&gt;We estimate the strike and dip of three California fault segments (Calaveras, Sargent, and a portion of the San Andreas near San Jaun Bautistia) based on principle component analysis of accurately located microearthquakes. We compare these fault orientations with two different first-motion focal mechanism catalogs: the Northern California Earthquake Data Center (&lt;/span&gt;&lt;span class="s2"&gt;NCEDC&lt;/span&gt;&lt;span class="s1"&gt;) catalog, calculated using the &lt;/span&gt;&lt;span class="s2"&gt;FPFIT&lt;/span&gt;&lt;span class="s1"&gt; algorithm (Reasenberg and Oppenheimer, 1985), and a catalog created using the &lt;/span&gt;&lt;span class="s2"&gt;HASH&lt;/span&gt;&lt;span class="s1"&gt; algorithm that tests mechanism stability relative to seismic velocity model variations and earthquake location (Hardebeck and Shearer, 2002). We assume any disagreement (misfit &amp;gt;30&amp;deg; in strike, dip, or rake) indicates inaccurate focal mechanisms in the catalogs. With this assumption, we can quantify the parameters that identify the most optimally constrained focal mechanisms. For the &lt;/span&gt;&lt;span class="s2"&gt;NCEDC/FPFIT&lt;/span&gt;&lt;span class="s1"&gt; catalogs, we find that the best quantitative discriminator of quality focal mechanisms is the station distribution ratio (&lt;/span&gt;&lt;span class="s2"&gt;STDR&lt;/span&gt;&lt;span class="s1"&gt;) parameter, an indicator of how the stations are distributed about the focal sphere. Requiring &lt;/span&gt;&lt;span class="s2"&gt;STDR&lt;/span&gt;&lt;span class="s1"&gt; &amp;gt; 0.65 increases the acceptable mechanisms from 34%&amp;ndash;37% to 63%&amp;ndash;68%. This suggests stations should be uniformly distributed surrounding, rather than aligning, known fault traces. For the &lt;/span&gt;&lt;span class="s2"&gt;HASH&lt;/span&gt;&lt;span class="s1"&gt; catalogs, the fault plane uncertainty (&lt;/span&gt;&lt;span class="s2"&gt;FPU&lt;/span&gt;&lt;span class="s1"&gt;) parameter is the best discriminator, increasing the percent of acceptable mechanisms from 63%&amp;ndash;78% to 81%&amp;ndash;83% when &lt;/span&gt;&lt;span class="s2"&gt;FPU&lt;/span&gt;&lt;span class="s1"&gt; &amp;le; 35&amp;deg;. The overall higher percentage of acceptable mechanisms and the usefulness of the formal uncertainty in identifying quality mechanisms validate the &lt;/span&gt;&lt;span class="s2"&gt;HASH&lt;/span&gt;&lt;span class="s1"&gt; approach of testing for mechanism stability.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1785/0120040239</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Seismological Society of America</dc:publisher>
  <dc:title>Fault parameter constraints using relocated earthquakes: A validation of first-motion focal-mechanism data</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>