Understanding the seafloor spreading cycle at the Endeavour Segment, Juan de Fuca Ridge using a multi-decadal microearthquake catalog

Abstract:

The Endeavour Segment is one of the most extensively studied sites on the global network of oceanic spreading centers. The segment last underwent a non-eruptive diking event between 1999 and 2005 that relieved extensional stress along the entire margin. With a full spreading rate of ~5 cm/yr and a typical dike width of ~1 m, the next Endeavour spreading event may occur fairly soon. Over 20 years of seismic observations at the ridge present the unique opportunity to construct a long-term microearthquake catalog capturing this full spreading cycle. For the past decade, Endeavour has been a node on the Ocean Networks Canada (ONC) NEPTUNE cabled observatory. The ONC Endeavour seismic observations commenced in 2011 with 1-2 stations and transitioned in 2016 to a network with stations at up to 4 sites. We present preliminary results of a study to develop an earthquake catalog for the ONC seismic network and reanalyze data from earlier ocean bottom seismometer experiments in 1995 and 2003-6 into a common framework. To accomplish this, we have explored the use of single station methods to analyze ONC data from 2011-2016 and have implemented an automated algorithm to obtain a near-real time earthquake catalog that extends from 2016 to the present. We are relocating all earthquakes using the NonLinLoc software and 3-D segment-scale models of P- and S-wave structure that have recently been obtained from a tomography experiment. The combined catalog comprises 3,300 earthquakes from the 1995 experiment, 36,500 (including dike-emplacement swarms) from the 2003-6 experiment and ~35,000 earthquakes from the ONC network. The use of NonLinLoc constrains significant non-linear location errors for many earthquakes and in some instances suggests that earthquakes were previously mislocated. The 3-D velocity models substantially modify the distribution of earthquakes in 1995 and 2003-6, leading to a better alignment of earthquakes with geological features. We plan to use statistical approaches to obtain a record of the rate of microearthquakes for the past decade that accounts for changes in the ONC network configuration. The complete catalog will present a cohesive long-term record of seismicity to characterize the buildup of strain on the Endeavour Segment and will eventually extend through a full eruptive cycle.