<?xml version='1.0' encoding='utf-8'?>
<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>W.H.K. Lee</dc:contributor>
  <dc:creator>R. D. Catchings</dc:creator>
  <dc:date>1996</dc:date>
  <dc:description>&lt;div id="130404884" class="article-section-wrapper js-article-section js-content-section  " data-section-parent-id="0"&gt;&lt;p&gt;The 17 January 1994, Northridge, California, earthquake produced strong ground shaking at the Cedar Hills Nursery (referred to here as the Tarzana site) within the city of Tarzana, California, approximately 6 km from the epicenter of the mainshock. Although the Tarzana site is on a hill and is a rock site, accelerations of approximately 1.78 g horizontally and 1.2 g vertically at the Tarzana site are among the highest ever instrumentally recorded for an earthquake. To investigate possible site effects at the Tarzana site, we used explosive-source seismic refraction data to determine the shallow (&amp;lt;70 m)&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;P&lt;/i&gt;-and&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;S&lt;/i&gt;-wave velocity structure. Our seismic velocity models for the Tarzana site indicate that the local velocity structure may have contributed significantly to the observed shaking.&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;P&lt;/i&gt;-wave velocities range from 0.9 to 1.65 km/sec, and&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;S&lt;/i&gt;-wave velocities range from 0.20 and 0.6 km/sec for the upper 70 m. We also found evidence for a local&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;S&lt;/i&gt;-wave low-velocity zone (&lt;span class="small-caps"&gt;LVZ&lt;/span&gt;) beneath the top of the hill. The&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="small-caps"&gt;LVZ&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;underlies a&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="small-caps"&gt;CDMG&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;strong-motion recording site at depths between 25 and 60 m below ground surface (&lt;span class="small-caps"&gt;BGS&lt;/span&gt;). Our velocity model is consistent with the near-surface (&amp;lt;30 m)&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;P&lt;/i&gt;- and&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;S&lt;/i&gt;-wave velocities and Poisson's ratios measured in a nearby (&amp;lt;30 m) borehole. High Poisson's ratios (0.477 to 0.494) and&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;S&lt;/i&gt;-wave attenuation within the&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="small-caps"&gt;LVZ&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;suggest that the&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="small-caps"&gt;LVZ&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;may be composed of highly saturated shales of the Modelo Formation. Because the lateral dimensions of the&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="small-caps"&gt;LVZ&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;approximately correspond to the areas of strongest shaking, we suggest that the highly saturated zone may have contributed to localized strong shaking. Rock sites are generally considered to be ideal locations for site response in urban areas; however, localized, highly saturated rock sites may be a hazard in urban areas that requires further investigation.&lt;/p&gt;&lt;/div&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1785/BSSA0860061704</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Seismological Society of America</dc:publisher>
  <dc:title>Shallow velocity structure and Poisson's ratio at the Tarzana, California, strong-motion accelerometer site</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>