Crustal anisotropy from tectonic tremor under Washington State in the Cascadia. Issue 7 (14th April 2015)

• Record Type: Journal Article
• Authors: Huesca‐Pérez, Eduardo; Ghosh, Abhijit
• Is Part Of: Geophysical research letters. Volume 42:Issue 7(2015:Apr.)
• Page Start: 2228
• Page End: 2234
• Publication Date: 2015-04-14
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2014GL062614
• Languages: English
• ISSNs: 0094-8276

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>We present new observations of crustal shear wave anisotropy extracted from nonvolcanic tremor in Cascadia under Washington State. Measurements of crustal anisotropy are extremely sparse and limited in this area mainly due to low level of seismicity. Abundance of tremor activity during slow earthquakes offers a unique opportunity to measure anisotropy parameters of the continental crust using tremor signal. To accomplish this, polarization and splitting analyses of nonvolcanic tremor are performed using three‐component broadband seismic stations. Splitting times measurements range between 0.08 and 0.17 s and similar to the splitting magnitude typically observed in the continental crust. Fast direction of shear wave anisotropy generally trends ESE‐WNW. Fast polarization directions are, in general, perpendicular to the prevailing maximum compressive stress field but tend to be parallel to several mapped EW and ESE‐WNW trending faults in this area. The observed spatial pattern of anisotropy is likely controlled by faulting that accommodates NS compression resulting from the tectonic movement of the Oregon block toward north. Existence of several EW trending crustal faults and source parameters of crustal earthquakes at depth, consistent with the regional stress regime, indicate that these faults may be the dominant factor causing the observed pattern of shear wave anisotropy.</p> </abstract>