Three‐dimensional seismic velocity structure of Mauna Loa and Kilauea volcanoes in Hawaii from local seismic tomography

Abstract

We present a new three‐dimensional seismic velocity model of the crustal and upper mantle structure for Mauna Loa and Kilauea volcanoes in Hawaii. Our model is derived from the first‐arrival times of the compressional and shear waves from about 53,000 events on and near the Island of Hawaii between 1992 and 2009 recorded by the Hawaiian Volcano Observatory stations. The Vp model generally agrees with previous studies, showing high‐velocity anomalies near the calderas and rift zones and low‐velocity anomalies in the fault systems. The most significant difference from previous models is in Vp/Vs structure. The high‐Vp and high‐Vp/Vs anomalies below Mauna Loa caldera are interpreted as mafic magmatic cumulates. The observed low‐Vp and high‐Vp/Vs bodies in the Kaoiki seismic zone between 5 and 15 km depth are attributed to the underlying volcaniclastic sediments. The high‐Vp and moderate‐ to low‐Vp/Vs anomalies beneath Kilauea caldera can be explained by a combination of different mafic compositions, likely to be olivine‐rich gabbro and dunite. The systematically low‐Vp and low‐Vp/Vs bodies in the southeast flank of Kilauea may be caused by the presence of volatiles. Another difference between this study and previous ones is the improved Vp model resolution in deeper layers, owing to the inclusion of events with large epicentral distances. The new velocity model is used to relocate the seismicity of Mauna Loa and Kilauea for improved absolute locations and ultimately to develop a high‐precision earthquake catalog using waveform cross‐correlation data.

Local earthquake tomography with the inclusion of full topography and its application to Kīlauea volcano, Hawai'i

“…Below 2 km depth, there is a high Vp zone (N7.0 km/s) at 5-14 km depth and high Vs zone (N3.9 km/s) at 5-11 km depth. This high Vp zone was also observed in previous studies (Dawson et al, 1999;Monteiller et al, 2005;Park et al, 2009;Lin et al, 2014) and was interpreted as consolidated intrusive gabbroultramafic cumulates (Okubo et al, 1997;Haslinger et al, 2001). The high Vs in this area also supports this interpretation.…”

“…All the inversion nodes are below the ground surface. The black dots represent the relocated seismicity within ± 0.5 km distance of the profile lines from a recent location catalog by Lin et al (2014). Zero depth again represents MSL.…”

“…The 1-D models are obtained by calculating the layer-average values of the 3-D velocity model from Lin et al (2014) and are also used as the initial models for both the synthetic and the real data inversions. The amplitudes of the anomalies are ±10% of the 1-D P-and S-wave velocity model, respectively.…”

“…(1)) for the inversion of P-and S-velocity models, separately. The strategy is similar to that described by Lin et al (2007) and Lin et al (2014). First, we fix λ s at a number as large as 25,000 to find the optimal λ p .…”

Dike model for the 2012–2013 Tolbachik eruption constrained by satellite radar interferometry observations

“…Seismicity prior to the GTE was much stronger and from mantle depths (>25 km) and is reflected in less silica rich basalt in 1975 relative to 2012 [Edwards et al, 2013]. The greater depth is also supported through the analysis of low-frequency microseisms that found evidence for anomalous seismic velocities extending beneath the area of activity in 1975-1976, whereas the area beneath the 2012-2014 fissures showed no such anomalies prior to the eruption [Kugaenko et al, 2013;Kugaenko et al, 2014].…”