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An integrated airborne gravity survey of an offshore area near the northern Noto Peninsula, Japan  

Komazawa, Masao (Geological Survey of Japan, AIST)
Okuma, Shigeo (Geological Survey of Japan, AIST)
Segawa, Jiro (Tokyo University of Marine Science and Technology)
Publication Information
Geophysics and Geophysical Exploration / v.13, no.1, 2010 , pp. 88-95 More about this Journal
Abstract
An airborne gravity survey using a helicopter was carried out in October 2008, offshore along the northern Noto Peninsula, to understand the shallow and regional underground structure. Eleven flight lines, including three tie lines, were arranged at 2 km spacing within 20 km of the coast. The total length of the flight lines was ~700 km. The Bouguer anomalies computed from the airborne gravimetry are consistent with those computed from land and shipborne gravimetry, which gradually decrease in the offshore direction. So, the accuracy of the airborne system is considered to be adequate. A local gravity low in Wajima Bay, which was already known from seafloor gravimetry, was also observed. This suggests that the airborne system has a structural resolution of ~2 km. Reduction of gravity data to a common datum was conducted by compiling the three kinds of gravity data, from airborne, shipborne, and land surveys. In the present study, we have used a solid angle numerical integration method and an iteration method. We finally calculated the gravity anomalies at 300 m above sea level. We needed to add corrections of 2.5 mGals in order to compile the airborne and shipborne gravity data smoothly, so the accuracy of the Bouguer anomaly map is considered to be nearly 2 mGal on the whole, and 5 mGals at worst in limited or local areas.
Keywords
airborne gravity survey; Bouguer anomalies; graben; Noto Peninsula; shipborne gravity survey; reduction to datum level; GRM; RCS;
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