@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 {RN217,
	title = {The mechanism of tidal triggering of earthquakes at mid-ocean ridges},
	journal = {Nature Communications},
	volume = {10},
	number = {1},
	year = {2019},
	pages = {2526},
	type = {Journal Article},
	abstract = {The strong tidal triggering of mid-ocean ridge earthquakes has remained unexplained because the earthquakes occur preferentially during low tide, when normal faulting earthquakes should be inhibited. Using Axial Volcano on the Juan de Fuca ridge as an example, we show that the axial magma chamber inflates/deflates in response to tidal stresses, producing Coulomb stresses on the faults that are opposite in sign to those produced by the tides. When the magma chamber{\textquoteright}s bulk modulus is sufficiently low, the phase of tidal triggering is inverted. We find that the stress dependence of seismicity rate conforms to triggering theory over the entire tidal stress range. There is no triggering stress threshold and stress shadowing is just a continuous function of stress decrease. We find the viscous friction parameter A to be an order of magnitude smaller than laboratory measurements. The high tidal sensitivity at Axial Volcano results from the shallow earthquake depths.},
	issn = {2041-1723},
	doi = {10.1038/s41467-019-10605-2},
	url = {https://doi.org/10.1038/s41467-019-10605-2},
	author = {Scholz, Christopher H. and Tan, Yen Joe and Albino, Fabien}
}
