Brian J. Olsen
Alex R. Grant
Jennifer R Andrews
Angela I. Chung
Susan E. Hough
Hiroo Kanamori
Sara K. McBride
Andrew J. Michael
Morgan T. Page
Zachary E. Ross
Deborah Smith
Sotiris Valkaniotis
Egill Hauksson
2021
<p><span>The 2020 </span><span class="inline-formula no-formula-id"><span id="MathJax-Element-3-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub xmlns=""><mi>M</mi><mi mathvariant="normal">w</mi></msub></math>"><span id="MathJax-Span-11" class="math"><span><span id="MathJax-Span-12" class="mrow"><span id="MathJax-Span-13" class="msub"><i><span id="MathJax-Span-14" class="mi">M</span></i><sub><span id="MathJax-Span-15" class="mi">w</span></sub></span></span></span></span></span></span><span> 5.8 Lone Pine earthquake, the largest earthquake on the Owens Valley fault zone, eastern California, since the nineteenth century, ruptured an extensional stepover in that fault. Owens Valley separates two normal‐faulting regimes, the western margin of the Great basin and the eastern margin of the Sierra Nevada, forming a complex seismotectonic zone, and a possible nascent plate boundary. Foreshocks began on 22 June 2020; the largest <span class="inline-formula no-formula-id"><span id="MathJax-Element-3-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub xmlns=""><mi>M</mi><mi mathvariant="normal">w</mi></msub></math>"><span id="MathJax-Span-11" class="math"><span id="MathJax-Span-12" class="mrow"><span id="MathJax-Span-13" class="msub"><i><span id="MathJax-Span-14" class="mi">M</span></i><sub><span id="MathJax-Span-15" class="mi">w</span></sub></span></span></span></span></span></span><span> 4.7 foreshock occurred at </span><span class="inline-formula no-formula-id"><span id="MathJax-Element-5-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo xmlns="" form="prefix">&#x223C;</mo><mn xmlns="">6</mn><mtext xmlns="">&#x2009;&#x2009;</mtext><mi xmlns="">km</mi></math>"><span class="MJX_Assistive_MathML">∼6 km</span></span></span><span> depth, with primarily normal faulting, followed </span><span class="inline-formula no-formula-id"><span id="MathJax-Element-6-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo xmlns="" form="prefix">&#x223C;</mo><mn xmlns="">40</mn><mtext xmlns="">&#x2009;&#x2009;</mtext><mi xmlns="">hr</mi></math>"><span id="MathJax-Span-27" class="math"><span><span id="MathJax-Span-28" class="mrow"><span id="MathJax-Span-29" class="mo">∼</span><span id="MathJax-Span-30" class="mn">40</span><span id="MathJax-Span-31" class="mtext"> </span><span id="MathJax-Span-32" class="mi">hr</span></span></span></span></span></span><span> later on 24 June 2020 by an <span class="inline-formula no-formula-id"><span id="MathJax-Element-3-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub xmlns=""><mi>M</mi><mi mathvariant="normal">w</mi></msub></math>"><span id="MathJax-Span-11" class="math"><span id="MathJax-Span-12" class="mrow"><span id="MathJax-Span-13" class="msub"><i><span id="MathJax-Span-14" class="mi">M</span></i><sub><span id="MathJax-Span-15" class="mi">w</span></sub></span></span></span></span></span></span><span> 5.8 mainshock at </span><span class="inline-formula no-formula-id"><span id="MathJax-Element-8-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo xmlns="" form="prefix">&#x223C;</mo><mn xmlns="">7</mn><mtext xmlns="">&#x2009;&#x2009;</mtext><mi xmlns="">km</mi></math>"><span id="MathJax-Span-38" class="math"><span><span id="MathJax-Span-39" class="mrow"><span id="MathJax-Span-40" class="mo">∼</span><span id="MathJax-Span-41" class="mn">7</span><span id="MathJax-Span-42" class="mtext"> </span><span id="MathJax-Span-43" class="mi">km</span></span></span></span></span></span><span> depth. The sequence caused overlapping ruptures across a </span><span class="inline-formula no-formula-id"><span id="MathJax-Element-9-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo xmlns="" form="prefix">&#x223C;</mo><mn xmlns="">0.25</mn><mtext xmlns="">&#x2009;&#x2009;</mtext><msup xmlns=""><mi>km</mi><mn>2</mn></msup></math>"><span class="MJX_Assistive_MathML">∼0.25 km<sup>2</sup></span></span></span><span> area, extended to </span><span class="inline-formula no-formula-id"><span id="MathJax-Element-10-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo xmlns="" form="prefix">&#x223C;</mo><mn xmlns="">4</mn><mtext xmlns="">&#x2009;&#x2009;</mtext><msup xmlns=""><mi>km</mi><mn>2</mn></msup></math>"><span id="MathJax-Span-52" class="math"><span><span id="MathJax-Span-53" class="mrow"><span id="MathJax-Span-54" class="mo">∼</span><span id="MathJax-Span-55" class="mn">4</span><span id="MathJax-Span-56" class="mtext"> </span><span id="MathJax-Span-57" class="msup"><span id="MathJax-Span-58" class="mi">km</span><sup><span id="MathJax-Span-59" class="mn">2</span></sup></span></span></span></span></span></span><span>, and culminated in an </span><span class="inline-formula no-formula-id"><span id="MathJax-Element-11-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo xmlns="" form="prefix">&#x223C;</mo><mn xmlns="">25</mn><mtext xmlns="">&#x2009;&#x2009;</mtext><msup xmlns=""><mi>km</mi><mn>2</mn></msup></math>"><span class="MJX_Assistive_MathML">∼25 km<sup>2</sup></span></span></span><span> aftershock area. The mainshock was predominantly normal faulting, with a strike of 330° (north‐northwest), dipping 60°–65° to the east‐northeast. Comparison of background seismicity and 2020 Ridgecrest aftershock rates showed that this earthquake was not an aftershock of the Ridgecrest mainshock. The <span class="inline-formula no-formula-id"><span id="MathJax-Element-3-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub xmlns=""><mi>M</mi><mi mathvariant="normal">w</mi></msub></math>"><span id="MathJax-Span-11" class="math"><span id="MathJax-Span-12" class="mrow"><span id="MathJax-Span-13" class="msub"><i><span id="MathJax-Span-14" class="mi">M</span></i><sub><span id="MathJax-Span-15" class="mi">w </span></sub></span></span></span></span></span></span><span class="inline-formula no-formula-id"><span id="MathJax-Element-12-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub xmlns=""><mi>M</mi><mi mathvariant="normal">w</mi></msub><mo xmlns="">&#x2013;</mo><msub xmlns=""><mi>m</mi><mi>B</mi></msub></math>"><span id="MathJax-Span-68" class="math"><span><span id="MathJax-Span-69" class="mrow"><span id="MathJax-Span-73" class="mo">– </span><span id="MathJax-Span-74" class="msub"><i><span id="MathJax-Span-75" class="mi">m</span></i><sub><span id="MathJax-Span-76" class="mi">B</span></sub></span></span></span></span></span></span><span> relationship and distribution of ground motions suggest typical rupture speeds. The aftershocks form a north‐northwest‐trending, north‐northeast‐dipping, 5 km long distribution, consistent with the rupture length estimated from analysis of regional waveform data. No surface rupture was reported along the 1872 scarps from the 2020 <span class="inline-formula no-formula-id"><span id="MathJax-Element-3-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub xmlns=""><mi>M</mi><mi mathvariant="normal">w</mi></msub></math>"><span id="MathJax-Span-11" class="math"><span id="MathJax-Span-12" class="mrow"><span id="MathJax-Span-13" class="msub"><i><span id="MathJax-Span-14" class="mi">M</span></i><sub><span id="MathJax-Span-15" class="mi">w</span></sub></span></span></span></span></span></span><span> 5.8 mainshock, although, the dipping rupture zone of the <span class="inline-formula no-formula-id"><span id="MathJax-Element-3-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub xmlns=""><mi>M</mi><mi mathvariant="normal">w</mi></msub></math>"><span id="MathJax-Span-11" class="math"><span id="MathJax-Span-12" class="mrow"><span id="MathJax-Span-13" class="msub"><i><span id="MathJax-Span-14" class="mi">M</span></i><sub><span id="MathJax-Span-15" class="mi">w</span></sub></span></span></span></span></span></span><span> 5.8 mainshock projects to the surface in the general area. The mainshock seismic energy triggered rockfalls at high elevations (</span><span class="inline-formula no-formula-id"><span id="MathJax-Element-15-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo xmlns="" form="prefix">&gt;</mo><mn xmlns="">3.0</mn><mtext xmlns="">&#x2009;&#x2009;</mtext><mi xmlns="">km</mi></math>"><span id="MathJax-Span-87" class="math"><span><span id="MathJax-Span-88" class="mrow"><span id="MathJax-Span-89" class="mo">></span><span id="MathJax-Span-90" class="mn">3.0</span><span id="MathJax-Span-91" class="mtext"> </span><span id="MathJax-Span-92" class="mi">km</span></span></span></span></span></span><span>) in the Sierra Nevada, at distances of 8–20 km, and liquefaction along the western edge of Owens Lake. Because there were </span><span class="inline-formula no-formula-id"><span id="MathJax-Element-16-Frame" class="MathJax" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo xmlns="" form="prefix">&#x223C;</mo><mn xmlns="">30</mn><mo xmlns="">%</mo></math>"><span id="MathJax-Span-93" class="math"><span><span id="MathJax-Span-94" class="mrow"><span id="MathJax-Span-95" class="mo">∼</span><span id="MathJax-Span-96" class="mn">30</span><span id="MathJax-Span-97" class="mo">% </span></span></span></span></span></span><span>fewer aftershocks than for an average southern California sequence, the aftershock forecast probabilities were lower than expected. ShakeAlert, the earthquake early warning system, provided first warning within 9.9 s, as well as subsequent updates.</span></p>
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10.1785/0220200324
en
Seismological Society of America
The normal faulting 2020 Mw5.8 Lone Pine, Eastern California earthquake sequence
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