TY - JOUR
T1 - Seismicity Relocation and Fault Structure Near the Leech River Fault Zone, Southern Vancouver Island
AU - Li, Ge
AU - Liu, Yajing
AU - Regalla, Christine
AU - Morell, Kristin D.
N1 - Funding Information:
We would like to thank Natalie Balfour and Taimi Mulder for providing valuable focal mechanism solutions, and Hongyu Yu for valuable discussions on using HypoDD. We also thank Christine Ruhl and an anonymous reviewer for their constructive comments that helped to improve the presentation of this manu script. This work is supported by the Fonds de recherche Nature et technol ogies Québec, Projet de recherche en équipe(191259) to Y. Liu at McGill, a National Science Foundation EAR IRFP (1349586) to C. Regalla at Boston U., and an NSERC Discovery Grant (RGPIN-2014-04260) to K. Morell at U.Vic. The original catalog earthquake hypocenters were downloaded from the Canadian National Seismograph Network (CNSN) (http://www.earthquakescanada.nrcan. gc.ca/stndon/NEDB-BNDS/bull-en.php). Catalog traveltimes were obtained via e-mail contact with CNSN staff.
Funding Information:
We would like to thank Natalie Balfour and Taimi Mulder for providing valuable focal mechanism solutions, and Hongyu Yu for valuable discussions on using HypoDD. We also thank Christine Ruhl and an anonymous reviewer for their constructive comments that helped to improve the presentation of this manuscript. This work is supported by the Fonds de recherche Nature et technologies Qu?bec, Projet de recherche en ?quipe(191259) to Y. Liu at McGill, a National Science Foundation EAR IRFP (1349586) to C. Regalla at Boston U., and an NSERC Discovery Grant (RGPIN-2014-04260) to K. Morell at U.Vic. The original catalog earthquake hypocenters were downloaded from the Canadian National Seismograph Network (CNSN) (http://www.earthquakescanada.nrcan.gc.ca/stndon/NEDB-BNDS/bull-en.php). Catalog traveltimes were obtained via e-mail contact with CNSN staff.
Publisher Copyright:
©2018. American Geophysical Union. All Rights Reserved.
PY - 2018/4
Y1 - 2018/4
N2 - Relatively low rates of seismicity and fault loading have made it challenging to correlate microseismicity to mapped surface faults on the forearc of southern Vancouver Island. Here we use precise relocations of microseismicity integrated with existing geologic data to present the first identification of subsurface seismogenic structures associated with the Leech River fault zone on southern Vancouver Island. We used the HypoDD double-difference relocation method to relocate 1,253 earthquakes reported by the Canadian National Seismograph Network catalog from 1992 to 2015. Our results reveal an ~8–10 km wide, NNE dipping zone of seismicity representing a subsurface structure along the eastern 30 km of the terrestrial Leech River fault zone and extending 20 km farther eastward offshore, where the fault bifurcates beneath the Juan de Fuca Strait. Using a clustering analysis, we identify secondary structures within the NNE dipping fault zone, many of which are subvertical and exhibit right-lateral strike-slip focal mechanisms. We suggest that the arrangement of these near-vertical dextral secondary structures within a more general NE dipping fault zone, located 10–15 km beneath the Leech River fault as imaged by LITHOPROBE, may be a consequence of the reactivation of this fault system as a right-lateral structure in crust with a preexisting NNE dipping structural fabric. Our results provide the first confirmation of active terrestrial crustal faults on Vancouver Island using a relocation method. We suggest that slowly slipping active crustal faults, especially in regions with preexisting foliations, may result in microseismicity along fracture arrays rather than along single planar structures.
AB - Relatively low rates of seismicity and fault loading have made it challenging to correlate microseismicity to mapped surface faults on the forearc of southern Vancouver Island. Here we use precise relocations of microseismicity integrated with existing geologic data to present the first identification of subsurface seismogenic structures associated with the Leech River fault zone on southern Vancouver Island. We used the HypoDD double-difference relocation method to relocate 1,253 earthquakes reported by the Canadian National Seismograph Network catalog from 1992 to 2015. Our results reveal an ~8–10 km wide, NNE dipping zone of seismicity representing a subsurface structure along the eastern 30 km of the terrestrial Leech River fault zone and extending 20 km farther eastward offshore, where the fault bifurcates beneath the Juan de Fuca Strait. Using a clustering analysis, we identify secondary structures within the NNE dipping fault zone, many of which are subvertical and exhibit right-lateral strike-slip focal mechanisms. We suggest that the arrangement of these near-vertical dextral secondary structures within a more general NE dipping fault zone, located 10–15 km beneath the Leech River fault as imaged by LITHOPROBE, may be a consequence of the reactivation of this fault system as a right-lateral structure in crust with a preexisting NNE dipping structural fabric. Our results provide the first confirmation of active terrestrial crustal faults on Vancouver Island using a relocation method. We suggest that slowly slipping active crustal faults, especially in regions with preexisting foliations, may result in microseismicity along fracture arrays rather than along single planar structures.
KW - clustering analysis
KW - earthquake relocation
KW - focal mechanisms
KW - forearc crustal structure
KW - waveform cross correlation
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U2 - 10.1002/2017JB015021
DO - 10.1002/2017JB015021
M3 - Article
AN - SCOPUS:85048052619
SN - 2169-9313
VL - 123
SP - 2841
EP - 2855
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
IS - 4
ER -