Study of mountain uplifting mechanism of Peruvian Andes

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We collected all the data of gravity measurements carried out over the last 40 years by Instituto Geofisico del Peru (IGP). Because of long time since the data collection, some of the important information needed for data reduction were lost in the mean time. For instance, it is not quite certain which constant table among several were applied to a particular to a particular survey conducted with a certain gravimeter. There were also other difficulties caused by the nature of the IGP dataset which became apparent to us in the course of conversion of the original data to gravity values. An example of this kind is that the measurement usually started at some point on the survey route and ended at another, so that it is difficult to find gravity stations correlatable to known references. Because of these problems, it was impossible to determine the gravity values unambiguously from the IGP data alone. Accordingly, there was a need for independently determined gravity stations to which the measurements done by IGP may be compared. In order to provide reference gravity values, we recalibrated the Japanese survey data obtained in 1980 and 1984, and conducted more surveys in various parts of Peru during the period from 1995 to 1998. These gravity stations number more than 800, and provide three or more reference points for each of the IGP survey routes. Using these references, the gravity values were calculated for the IGP dataset and Bouguer corrections were applied. Finally we established more than 10,000 gravity values in all survey routes and a Bouguer anomaly map of whole Peru was successfully produced based on these data.