GPS‐positioned gravity survey of Guadalupe Island, Mexico

Global Positioning System (GPS) meaSuremenu formed an easential lxut of a land gravity survey conducted on Guadalupe Island, Mexico, during March of 1991. Kinematic load and coastline surveys using C/A code derived positions proviaed reference navigation for most of the geologic-geophysical f eldwc& A tluee-station geod&networkwasalsoe&blishedontheislaad. Wedetem&d intra4sIand awl regional baselinea fnnn 9 days of GPS obsevatimu using improved global orbits. Onshore gravity trnverscs waz positioned relative to the geodetic monuments with rapid-static, arrier phase methods to permit high-accuracy reduction of gmvimeter readings. 1169 technique impmves the quality of calculated gravity anomalies that BTC essendal to determine local density anomalies and the island% undalying isosUic compensation mechsnii. During 12 days on the island we conducted a 126-&e land gravity smvey that sampled the on-shore gravity field from sea level to Ihe summit of the island’s shield volcano& From gravimetric methods we estimated the &rage density of Guadahp’ s younger volcanic editice to he 2560 f 80 kn m”. The density of the older. more heavily wdhnented so& vdcano is 2tMO 2 100 kg mm3. Over the southem shield volcano, terraincorrected Bouguer anomalies of maximum amplitude 15 f 3 mGal may be associated with discontinuous regions of low density material.