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Loura Seif
The geological structures in the study area are dominated by faults. The rest directions of the faults are northeast-southwest (16 faults) and north-south (14 faults). The remainder of faults are trending in northwest-southeast (3 faults) and west-east (3 faults) directions. Generally, the northeast-southwest and north-south trending faults are dominated by sinitral faults and a few of them are reactivated as normal faults. Whereas the northwest-southeast and west-east trending faults are mainly dextral and or normal faults.
We conducted a research to determine the appropriate method of separation of regional residual anomalies and made a subsurface model of Surakarta city. The gravity survey was done in 2010 as part of land subsidence survey campaign in Surakarta. Three methods were used in the separation of regional-residual anomaly i.e. moving average, polynomial, and inversion. The polynomial method is in order 1st to 5th. The residual anomaly in 3rd order of the polynomial is the best result and we made a model from this contour values. The results of the model contain three layers, the first layer has a density of 1.74 gr/cm3 which is sand. The second and third layer has a density of 2.10 gr/cm3 and 2.24 gr/cm3, respectively, with both are related to sandstones.