Stress Change on Faults at Kīlauea Volcano from an Intrusive Event in April-May, 2015

Abstract:

The magmatic and tectonic systems at Kīlauea Volcano are intimately connected; both magma movement and fault slip change the stress field in the surrounding crust and are themselves sensitive to these changes. An example of this occurred during the 2007 Father’s Day eruption, when a dike intrusion induced an expected slow slip event on the décollement. As a result, fault motion stimulated further dike emplacement. Here, we examine stress change on Kīlauea’s faults due to a series of magmatic events in April-May, 2015. In particular, we look at the effect on the Koa`e fault system, a series of north-facing normal faults south of the caldera, extending from the upper East Rift Zone (ERZ) to the Southwest Rift Zone, that produces both earthquakes and fault creep. The April-May sequence began with inflation near Halema`uma`u (HMM) Crater over a few weeks, followed by HMM deflation coincident with inflation of a source in the south caldera over a few days. The initial inflation period was marked by a rise in the level of the lava lake hosted within an eruptive vent in HMM Crater, to the point where it overflowed onto the crater floor. This was accompanied by elevated rates of seismicity in the upper ERZ and south caldera. In the later phase, the lava level dropped and upper ERZ seismicity declined, but south caldera seismicity intensified. We use the Coulomb 3 software to calculate stress changes from a source model that is based on high-rate data from a volcano-wide network of tiltmeters and GPS stations, as well as several independent interferograms from multiple satellites. While the complexity of the April-May event in both space and time represents a significant challenge for constructing a source model, our aim is to understand the how various approaches might affect stress transfer onto nearby fault systems, and thereby improve our understanding of the potential interplay between intrusive events such as this and fault slip.