@article {barkat_permeability_2024,
	title = {Permeability and seismicity rate changes at an inflating submarine volcano caused by dynamic stresses},
	journal = {Earth and Planetary Science Letters},
	volume = {632},
	year = {2024},
	pages = {118625},
	abstract = {Transient stresses from the passage of seismic waves are known to trigger earthquakes and cause crustal permeability changes. However, whether permeability change is a main driver of dynamic earthquake triggering remains debated. Our understanding of the characteristics of dynamic triggering in submarine volcanic environments is also limited due to the lack of offshore observations. Here, we utilize a high-resolution micro-seismicity catalog from July 2015 to July 2022 to evaluate the triggering response of Axial Seamount, an inflating and seismically active submarine volcano located in the northeast Pacific Ocean. We report statistically significant episodes of dynamic earthquake triggering for \~{}18 \% of the teleseismic events investigated, which is comparable with subaerial tectonic and volcanic environments. We do not observe any obvious dependence of triggering rate on the amplitude of peak ground velocity. However, a comparison of the triggering rate and the cumulative magma volume shows that the triggering susceptibility might increase as the volcano becomes more critically stressed. Using data recorded by a temperature sensor in a black smoker, we compute the phase lag between hydrothermal vent-fluid temperature and tidal loading amplitude before and after the arrival of teleseismic waves to probe the relationship between permeability change and dynamic triggering. While the energy density thresholds for dynamic earthquake triggering and permeability change are comparable, both triggering and non-triggering observations show similar proportions of permeability changes. Our results suggest that permeability change induced by transient stresses might not be a necessary or primary mechanism that drives dynamic earthquake triggering.},
	keywords = {Dynamic earthquake triggering, Permeability changes, Transient stresses, Volcanic inflation},
	issn = {0012-821X},
	doi = {10.1016/j.epsl.2024.118625},
	url = {https://www.sciencedirect.com/science/article/pii/S0012821X2400058X},
	author = {Barkat, Adnan and Tan, Yen Joe and Xu, Guangyu and Waldhauser, Felix and Tolstoy, Maya and Wilcock, William S. D.}
}
@article {RN66,
	title = {Axial Seamount: Periodic tidal loading reveals stress dependence of the earthquake size distribution (b value)},
	journal = {Earth and Planetary Science Letters},
	volume = {512},
	year = {2019},
	pages = {39-45},
	type = {Journal Article},
	abstract = {Earthquake size-frequency distributions commonly follow a power law, with the b value often used to quantify the relative proportion of small and large events. Laboratory experi13 ments have found that the b value of microfractures decreases with increasing stress. Stud14 ies have inferred that this relationship also holds for earthquakes based on observations of earthquake b values varying systematically with faulting style, depth, and for subduction zone earthquakes, plate age. However, these studies are limited by small sample sizes de17 spite aggregating events over large regions, which precludes the ability to control for other variables that might also affect earthquake b values such as rock heterogeneity and fault roughness. Our natural experiment in a unique seafloor laboratory on Axial Seamount involves analyzing the size-frequency distribution of \~{}60,000 microearthquakes which
delineate a ring-fault system in a 25 km3 21 block of crust that experiences periodic tidal loading of {\textpm}20 kPa. We find that above a threshold stress amplitude, b value is inversely correlated with tidal stress. The earthquake b value varies by \~{}0.09 per kPa change in Coulomb stress. Our results support the potential use of b values to estimate small stress variations in the Earth{\textquoteright}s crust.},
	issn = {0012-821X},
	doi = {10.1016/j.epsl.2019.01.047},
	url = {http://www.sciencedirect.com/science/article/pii/S0012821X19300731},
	author = {Tan, Yen Joe and Waldhauser, Felix and Tolstoy, Maya and Wilcock, William S. D.}
}
@article {RN122,
	title = {A Joint Inversion for Three-dimensional P and S Wave Velocity Structure and Earthquake Locations Beneath Axial Seamount},
	journal = {Journal of Geophysical Research: Solid Earth},
	volume = {n/a},
	number = {n/a},
	year = {2019},
	type = {Journal Article},
	abstract = {Axial Seamount is a prominent volcano located at the intersection of the Juan de Fuca Ridge and the Cobb-Eickelberg hot spot in the northeast Pacific Ocean that has erupted in 1998, 2011, and 2015. The 2015 eruption was recorded by a seven-station seismic network in the southern part of the summit caldera that forms part of the Ocean Observatories Initiative Cabled Array. We utilize a data set of ~3,900 well-recorded earthquakes from January 2015 to February 2017 and a three-dimensional P wave velocity model obtained previously from active source data to conduct a joint inversion for three-dimensional P and S wave velocities and hypocentral parameters. The resulting velocity models are used to relocate >76,000 earthquakes with >=10 arrival times. The velocity models reveal a low-velocity anomaly in the center of the southern caldera at depths less than ~2 km, which corresponds to the top of the magma chamber and is interpreted as a region that is intensely fractured by the cyclical deformation of the caldera. High velocities around the caldera rim are likely due to consolidated undeformed lava flows. Low VP/VS in the southern caldera is consistent with the presence of hydrothermal vapor. Low S wave velocities and high VP/VS in the northern caldera may indicate a region dominated by thin cracks caused by dike injection. The relocated earthquakes delineate outward-dipping ring faults more clearly than previous studies and image a subvertical inward-dipping fault within the network that connects to the east caldera wall and eruptive fissures.},
	keywords = {axial seamount, Earthquakes location, Hydrothermal systems, Joint inversion, Tomography, volcano},
	issn = {2169-9313},
	doi = {10.1029/2019JB017970},
	author = {Baillard, Christian and Wilcock, William S. D. and Arnulf, Adrien F. and Tolstoy, Maya and Waldhauser, Felix}
}
