Seismic and Geodetic Observations of Recent Unrest at Mauna Loa Volcano

Abstract:

Mauna Loa, the largest active volcano on Earth, has exhibited signs of unrest consisting of increased seismicity beginning in March 2013 and slow inflation starting in early 2014. A previous episode of unrest occurred during 2002–2009, with swarms of deep long-period (DLP) earthquakes at >30 km depth and inflationary deformation. Mauna Loa is currently in the longest period of repose in the last 200 years, its last eruption having occurred in 1984.

Seismic precursors to eruptions of Mauna Loa eruptions in 1975 and 1984 included episodic volcano-tectonic (VT) events centered northwest of the summit at depths of ~7 km and to the south of the caldera at <5 km depth. Current seismic activity, which has also been episodic, has also consisted of VT events occurring in similar locations, but with much lower energy release than the 1975 and 1984 seismic activity. Beginning in late May 2014, there was also an increase in the occurrence of DLP events. While approaching the numbers of earthquakes seen during the 2002 swarm (31 events) the current number of DLPs thus far pales in comparison to the 2004-2005 swarm (2000 events). As of July 2014, subtle inflationary deformation is apparent in both InSAR and GPS data, although inflation rates are much less than those observed in the several years preceding and following the 1984 eruption, and also far less than during the height of the 2002-2009 unrest. The inflation is consistent with pressurization of the known 3-5-km-deep magma storage area beneath Mauna Loa’s caldera.

Seismic event rates and deformation, though smaller in magnitude, are similar to the precursory activity seen in 1975 and 1984. Careful tracking of the current unrest by recently upgraded seismic and geodetic monitoring, regardless of whether or not it culminates in eruption, offers excellent prospects for unraveling Mauna Loa’s magma plumbing system and structure. In this presentation we will give a synoptic view of unrest associated with Mauna Loa as recorded on a recently upgraded seismic and geodetic monitoring network.