GEODETIC ANALYSIS OF DIKE INTRUSION AND MOTION OF THE MAGMA RESERVOIR BENEATH THE SUMMIT OF KILAUEA VOLCANO, HAWAII - 1970-1985

We use leveling and trilateration data collected on Kilauea volcano to constrain the location of deformation sources caused by magma accumulation, intrusion, and eruption. For the 13 inflationary epochs examined, combinations of an expanding point source and one or two opening rectangular dislocations mimic inflation of the summit reservoir and formation of dike(s), respectively. The combined model adequately accounts for the deformation data and is consistent with the seismicity observed during epoch. For 10 deflationary epochs, however, the data require only a contracting point source. Confidence in these results is gained by noting that locations of the sources of both inflation and deflation are coincident, within the observed uncertainties of the data, the function of network geometry, and the inversion procedure. It appears, therefore, that magma accumulation at Kilauea volcano may be characterized by the growth of dikes during inflation of the summit reservoir. Drainage of the reservoir, on the other hand, is not accompanied by significant closure of dikes. In contrast to previous studies (e.g., Fiske and Kinoshita, 1969; Dvorak et al., 1983) that do not include the dislocation (or dike growth) component of summit magma accumulation and concluded that the source of inflation migrates over a 5 km2 area, we find that a single magmatic reservoir source accounts for data collected during all inflationary and deflationary epochs, results, which compare favorably with those obtained from the point ellipsoid model, can be used to estimate the distribution of stresses within the volcano in the near field of the source.