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Microearthquake evidence for reaction‐driven cracking within the Trans‐Atlantic Geotraverse active hydrothermal deposit
Author(s) -
Pontbriand Claire W.,
Sohn Robert A.
Publication year - 2014
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2013jb010110
Subject(s) - microearthquake , hydrothermal circulation , geology , geochemistry , cracking , seismology , oceanography , materials science , composite material , induced seismicity
We detected 32,078 very small, local microearthquakes (average M L = −1) during a 9 month deployment of five ocean bottom seismometers on the periphery of the Trans‐Atlantic Geotraverse active mound. Seismicity rates were constant without any main shock‐aftershock behavior at ~243 events per day at the beginning of the experiment, 128 events per day after an instrument failed, and 97 events per day at the end of the experiment when whale calls increased background noise levels. The microearthquake seismograms are characterized by durations of <1 s and most have single‐phase P wave arrivals (i.e., no S arrivals). We accurately located 6207 of the earthquakes, with hypocenters clustered within a narrow depth interval from ~50 to 125 m below seafloor on the south and west flanks of the deposit. We model the microearthquakes as reaction‐driven fracturing events caused by anhydrite deposition in the secondary circulation system of the hydrothermal mound and show that under reasonable modeling assumptions an average event represents a volume increase of 31–58 cm 3 , yielding an annual (seismogenic) anhydrite deposition rate of 27–51 m 3 .