GTOOLS: an Interactive Computer Program to Process Gravity Data for High-Resolution Applications

An interactive computer program, GTOOLS, has been developed to process gravity data acquired by the Scintrex CG-5 and LaCoste & Romberg EG, G and D gravity meters. The aim of GTOOLS is to provide a validated methodology for computing relative gravity values in a consistent way accounting for as many environmental factors as possible (e.g., tides, ocean loading, solar constraints, etc.), as well as instrument drift. The program has a modular architecture. Each processing step is implemented in a tool (function) that can be either run independently or within an automated task. The tools allow the user to (a) read the gravity data acquired during field surveys completed using different types of gravity meters; (b) compute Earth tides using an improved version of Longman’s (1959) model; (c) compute ocean loading using the HARDISP code by Petit and Luzum (2010) and ocean loading harmonics from the TPXO7.2 ocean tide model; (d) estimate the instrument drift using linear functions as appropriate; and (e) compute the weighted least-square-adjusted gravity values and their errors. The corrections are performed up to microGal ( μGal) precision, in accordance with the specifications of high-resolution surveys. The program has the ability to incorporate calibration factors that allow for surveys done using different gravimeters to be compared. Two additional tools (functions) allow the user to (1) estimate the instrument calibration factor by processing data collected by a gravimeter on a calibration range; (2) plot gravity time-series at a chosen benchmark. The interactive procedures and the program output (jpeg plots and text files) have been designed to ease data handling and archiving, to provide useful information for future data interpretation or modeling, and facilitate comparison of gravity surveys conducted at different times. All formulas have been checked for typographical errors in the original reference. GTOOLS, developed using Matlab, is open source and machine independent. We will demonstrate program use and utility with data from multiple microgravity surveys at Kilauea volcano, Hawai’i

Magnetotelluric Investigations of the Kīlauea Volcano, Hawaii

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

Geoelectric studies on the East Rift, Kilauea Volcano, Hawaii island

Three geophysical research organizations, working together under the auspices of the Hawaii Geothermal Project, have used several electrical and electromagnetic exploration techniques on Kilauea volcano, Hawaii to assess its geothermal resources. This volume contains four papers detailing their methods and conclusions. Keller et al. of the Colorado School of Mines used the dipole mapping and time-domain EM sounding techniques to define low resistivity areas around the summit and flanks of Kilauea. Kauahikaua and Klein of the Hawaii Institute of Geophysics then detailed the East Rift with independent, two-loop induction and time-domain EM soundings. Finally, Zablocki of the U. S. Geological Survey delineated four anomalous areas on the East Rift with an extensive self-potential survey; one of these areas was chosen as the site of a test hole.Funded by grants from the National Science Foundation (GI-38319) and the Energy Research Development Administration, Grant E(04-3)-1093.Electrical resistivity and time-domain electromagnetic surveys of the Puna and Kau districts, Hawaii County, Hawaii / G. V. Keller, C. K. Skokan, J. J. Skokan, and J. Daniels -- Electromagnetic induction sounding measurements / J. P. Kauahikaua and Douglas P. Klein -- Interpretation of electromagnetic transient soundings made on the East Rift of Kilauea Volcano, Hawaii / J. P. Kauahikaua and Douglas P. Klein -- Self-potential studies in East Puna, Hawaii / C. J. Zablock