Lawrence Berkeley National Laboratory

Abstract In 2002 and 2003 a collaborative effort was undertaken between Lawrence Berkeley National Laboratory, Sandia National Laboratories, the U.S. Geological Survey (USGS) Menlo Park, the USGS Hawaiian Volcano Observatory, and Electromagnetic Instruments Inc. to study the Kīlauea volcano in Hawaii using the magnetotelluric (MT) technique. The work was motivated by a desire to improve understanding of the magma reservoirs and conduits within Kīlauea and the East and Southwest Rift zones, which has implications for understanding Kīlauea's plumbing system. An improved understanding of the rift zones has implications in understanding large‐scale landslides that are generated in the Hilina Slump, which produce significant impacts on coastal communities. Up to eight stations operated simultaneously, with multiple remote reference sites, and data were processed using multi‐station robust processing techniques. In total, data were acquired at 70 sites over the Southwest and East rift zones. Good to excellent quality data were obtained even in the harshest conditions, such as those encountered on the fresh lava flows of the East Rift Zone, where electrical contact resistances are on the order of 100 kΩ. A three‐dimensional (3D) MT model study was done to guide interpretation of the observed MT measurements. Synthetic modeling demonstrates that conductive bodies in the upper 3 km can be spatially resolved where MT station sampling is good. Resistivity anomalies in the 3D inversions have a high degree of spatial correlation with previously published seismic velocity anomalies beneath Kīlauea. Melt fractions between 0.096 and 0.117 are calculated for the Kīlauea and Puʻuʻōʻō low resistivity anomalies, respectively. Plain Language Summary Magnetotelluric (MT) data collected on the Island of Hawaiʻi on Kīlauea volcano and its associated rift zones in 2002 and 2003 have been inverted to produce a three‐dimensional resistivity model. The resistivity model is compared to published models of seismic velocity and Vp/Vs ratio derived from earthquake data acquired by the Hawaiian Volcano Observatory. In areas where the velocity models have good data coverage and high sensitivity, such as over the summit magma chamber, the MT derived resistivity, and the seismic derived Vp and Vp/Vs models have a very high degree of spatial correlation. The high correlation between independent models increases the confidence in both models. Melt fractions of 0.096 and 0.117 are calculated from the inverted resistivities for low resistivity anomalies beneath Kīlauea and Puʻuʻōʻō respectively. This work demonstrates that high‐quality MT data can be acquired in the difficult field conditions present on an active volcano and points the way forward for future improved acquisitions. Key Points Inverted three‐dimensional (3D) resistivity has high spatial correlation with seismic Vp/Vs from Dawson et al. (1999) Melt fractions of 0.096 and 0.117 are predicted for magma bodies beneath Kīlauea and Puʻuʻōʻō respectively The Kīlauea summit magma chamber is well imaged between 0 and −2 km elevations by 3D resistivity