Gravity observations on Santorini island (Greece): Historical and recent campaigns

Santorini is located in the central part of the Hellenic Volcanic Arc (South Aegean Sea) and is well known for the Late-Bronze-Age “Minoan” eruption that may have been responsible for the decline of the great Minoan civilization on the island of Crete. To use gravity to probe the internal structure of the volcano and to determine whether there are temporal variations in gravity due to near surface changes, we construct two gravity maps. Dionysos Satellite Observatory (DSO) of the National Technical University of Athens (NTUA) carried out terrestrial gravity measurements in December 2012 and in September 2014 at selected locations on Thera, Nea Kameni, Palea Kameni, Therasia, Aspronisi and Christiana islands. Absolute gravity values were calculated using raw gravity data at every station for all datasets. The results were compared with gravity measurements performed in July 1976 by DSO/NTUA and absolute gravity values derived from the Hellenic Military Geographical Service (HMGS) and other sources. Marine gravity data that were collected during the PROTEUS project in November and December 2015 fill between the land gravity datasets. An appropriate Digital Elevation Model (DEM) with topographic and bathymetric data was also produced. Finally, based on the two combined datasets (one for 2012–2014 and one for the 1970s), Free air and complete Bouguer gravity anomaly maps were produced following the appropriate data corrections and reductions. The pattern of complete Bouguer gravity anomaly maps was consistent with seismological results within the caldera. Finally from the comparison of the measurements made at the same place, we found that, within the caldera, the inner process of the volcano is ongoing both before, and after, the unrest period of 2011–2012.

A Comparative Study on Two Different Methods for Calculating Gravity Effect of an Uneven Layer: Application to Computation of Bouguer Gravity Anomaly in the East Vietnam Sea and Adjacent Areas

Calculation of gravity anomaly caused by an uneven layer is essential for quantitative interpretation. By comparing calculated anomalies with observed anomalies, we may infer some parameters of subsurface structures. There are many different methods for computing gravity effect of an uneven layer. This paper presents a comparative study of two different forward methods such as the space domain method and the frequency domain method. The performance of each method was evaluated on two synthetic models. Finally, the more effective method was applied to calculate Bouguer gravity anomaly in the East Vietnam Sea and adjacent areas using the latest available dataset from the TOPEX mission.

Plate and faults boundary detection using gravity disturbance and Bouguer gravity anomaly from space geodesy

Nowadays, satellite technology has developed significantly. Geodesy satellites such as Grace and Grace-FO can be used for subsurface mapping. The mapping is in the form of detection of the plate details, faults, and regional geodynamic conditions. This study aims to detect plate and faults from space geodesy using the gravity disturbance and Bouguer gravity anomaly parameter. The study area is in the Sunda Strait. Gravity disturbance is one of the gravity model parameters. Gravity disturbance is the gravitational potential of the topography expressed by the spherical harmonic model and the topographic effect by Barthelmes's calculations. Gravity disturbance can visualize subsurface conditions. Bouguer gravity anomaly is needed to get the condition on subsurface objects. This parameter visualizes subsurface conditions in the form of rocks and non-rocks. These conditions can distinguish oceanic crust and continental crust. Gravity contours are needed to obtain plate and faults predictions. The results obtained are validated patterns and shapes with plate and faults secondary data. The tolerance used in this validation is 80%. The gravity disturbance parameter obtained a value of 83% in verifying the accuracy of assessment in plate and faults detection. The Bouguer gravity disturbance parameter obtained a verification value of accuracy assessment in plate detection but 65% in faults detection. This accuracy assessment uses pattern and texture parameters in detecting the similarity of two or more images. This plate and faults detection results are more detailed and can be used for geophysical, geological, earthquake, and earth dynamics applications.

Study on distribution features of faults based on gravity data in the Gulf of Mexico and its adjacent areas

<p>In the study of Gulf of Mexico and its adjacent areas, the faults are kinds of important structures in the plate tectonics, oceanic-continental distribution and sedimentary basin structure. Based on the normalized vertical derivative of total horizontal derivative (NVDR-THDR) of Bouguer gravity anomaly and the minimum curvature field separation method, the distribution characteristics of the faults and the relating geological effects are studied. Because of the interaction between the plates, at the plate margin, the maximum values in the map of NVDR-THDR of Bouguer gravity anomaly are characterized by stable and continuous strikes. The maximum values in the map of NVDR-THDR of Bouguer gravity anomaly of intraplate region are macroscopically consistent and locally discontinuous. The faults in NWW and EW-NEE directions are mostly related to plate movement. In NE-NEE directions, arc faults are related to oceanic crust expansion. The faults in NE and NW are related to late Jurassic rift activities, or simply showing the boundaries of Yucatan and Chortis old landmass. The faults in nearly SN direction are less than that of we have talked above. In the Gulf of Mexico, there are four kinds of faults: the transition faults and mid-ocean ridge faults in the middle of central deep-sea area, the ocean-crust boundary faults in the north and south side of the central deep-sea area, the faults of thinning continental crust in the north and south of the Gulf of Mexico and the strike slip faults in the west of the Gulf of Mexico. Our research can contribute to regional geological researches and natural resources evaluations.</p>