Broadband Synthetic Seismograms for Magnitude 9 Earthquakes on the Cascadia Megathrust Based on 3D Simulations and Stochastic Synthetics, Part 2: Rupture Parameters and Variability

Abstract

Research Article| August 07, 2018 Broadband Synthetic Seismograms for Magnitude 9 Earthquakes on the Cascadia Megathrust Based on 3D Simulations and Stochastic Synthetics, Part 2: Rupture Parameters and Variability Erin A. Wirth; Erin A. Wirth aU.S. Geological Survey, University of Washington, Box 351310, Seattle, Washington 98195, [e-mail] at Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, Washington 98195. Search for other works by this author on: GSW Google Scholar Arthur D. Frankel; Arthur D. Frankel aU.S. Geological Survey, University of Washington, Box 351310, Seattle, Washington 98195, [e-mail] Search for other works by this author on: GSW Google Scholar Nasser Marafi; Nasser Marafi bDepartment of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar John E. Vidale; John E. Vidale cSouthern California Earthquake Center, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089eFormerly at Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, Washington 98195. Search for other works by this author on: GSW Google Scholar W. J. Stephenson W. J. Stephenson dU.S. Geological Survey, Box 25046, DFC, MS 966, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information Erin A. Wirth aU.S. Geological Survey, University of Washington, Box 351310, Seattle, Washington 98195, [e-mail] at Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, Washington 98195. Arthur D. Frankel aU.S. Geological Survey, University of Washington, Box 351310, Seattle, Washington 98195, [e-mail] Nasser Marafi bDepartment of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, Washington 98195 John E. Vidale cSouthern California Earthquake Center, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089eFormerly at Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, Washington 98195. W. J. Stephenson dU.S. Geological Survey, Box 25046, DFC, MS 966, Denver, Colorado 80225 Publisher: Seismological Society of America First Online: 07 Aug 2018 Online Issn: 1943-3573 Print Issn: 0037-1106 © Seismological Society of America Bulletin of the Seismological Society of America (2018) 108 (5A): 2370–2388. https://doi.org/10.1785/0120180029 Article history First Online: 07 Aug 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Erin A. Wirth, Arthur D. Frankel, Nasser Marafi, John E. Vidale, W. J. Stephenson; Broadband Synthetic Seismograms for Magnitude 9 Earthquakes on the Cascadia Megathrust Based on 3D Simulations and Stochastic Synthetics, Part 2: Rupture Parameters and Variability. Bulletin of the Seismological Society of America 2018;; 108 (5A): 2370–2388. doi: https://doi.org/10.1785/0120180029 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract We used a combination of 3D finite‐difference simulations (⁠<1 Hz⁠) and 1D stochastic synthetics (⁠>1 Hz⁠) to generate broadband (0–10 Hz) synthetic seismograms for numerous Mw 9 earthquake rupture scenarios on the Cascadia megathrust. Slip consists of multiple high‐stress‐drop subevents (⁠Mw 8) with short rise times on the deeper portions of the fault, superimposed on a background slip distribution with longer rise times. We identify key rupture parameters that control the intensity of ground shaking and resulting seismic hazard; these include the hypocenter location, the down‐dip limit of slip, the average rupture velocity, and the character (i.e., location, magnitude, and stress drop) of subevents. Extending the down‐dip limit of rupture to the top of the nonvolcanic tremor zone results in localized regions with a factor of 5–10 increase in spectral acceleration (SA) for periods <5 s⁠, compared to a rupture that is completely offshore. This is primarily due to the closer proximity of high‐stress‐drop subevents to inland locations when the rupture is allowed to extend deeper. Similarly, we find that the hypocenter location can result in a variation in the intensity of ground motions of a factor of >10⁠, due to the effects of rupture directivity (i.e., SA at periods >1 s⁠). We also observe a coupling between rupture directivity and basin amplification. The intensity of ground motions is also strongly affected by the magnitude, stress drop, and location of high‐stress‐drop subevents, which are poorly constrained. Overall, our results quantify the effect of kinematic rupture parameters on ground motions for an Mw 9 earthquake in Cascadia and emphasize the need for further constraints on these parameters to improve seismic hazard estimates in the Pacific Northwest. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.