Relocation of long-period (LP) seismic events reveals en echelon fractures in the upper edifice of Turrialba volcano, Costa Rica

Swarms of long-period (LP) events were recorded on Turrialba volcano, Costa Rica, during a seismic field experiment in 2009. Families of LP events were previously identified and located using a joint inversion for source location and mechanism; however, the spatial resolution of the obtained locations was not sufficient for imaging the structures on which they occur. Using a waveform similarity-based location method, we take advantage of the joint location-mechanism inversion by relocating events around the obtained familial location. The location method is successfully tested on a synthetic data set and is then applied to the Turrialba LP data set. The relocated events are jointly interpreted with their source mechanisms and reveal an en echelon structure within the upper edifice of the volcano. This can be interpreted as a response of a shearing band with high fluid pressure inducing tensile fractures at unconsolidated rock layer interfaces within the upper edifice of the volcano.