Eruption Dynamics and Variations in Earthquake Stress Drop With the 2015 Eruption of Axial Seamount

Date: 4/26/2019

Time: 06:00 PM

Room: Fifth Avenue

The Ocean Observatory Initiative Cabled Array at Axial Seamount on the Juan de Fuca Ridge captures an unprecedented amount of geophysical, chemical, and biological data associated with submarine volcanism in real time. The cabled array includes seven ocean bottom seismometers located within and along the caldera that recorded the intense seismicity (including more than 100,000 earthquakes between January 2015 and November 2017) associated with the most recent eruption of Axial in April and May 2015. We use this unique seismic data to investigate how crustal strength, inferred from earthquake stress drop, evolves with seafloor deformation and magmatic processes before, during, and after the 2015 eruption.

We calculate stress drops between 0.07 – 9.4 MPa from corner frequency derived using an empirical Green’s function spectral ratio method for 249 earthquakes (1.1 < M_W < 3.2) located within the caldera near the cabled array. We use strict pairing and modeling criteria for spectral ratios, and further examine earthquakes with M_W 1.7 – 2.5 to ensure that noise is well-outside the range of observed corner frequencies. We focus on a subset of 79 earthquakes in the northeast caldera where lava flows indicate dike intrusion. We find stress drops between 0.09 – 8.4 MPa for these events and 1.8 times higher average stress drop during inflation than deflation. This difference in stress drop is not statistically significant, and likely reflects increased hydrothermal fluid flow before and during the eruption; with slightly decreased crustal strength during magma ascent and deflation.

Presenting Author: Pamela Moyer

Authors