Magnetic method in geophysical surveys is common for its non-destructive use of sub-surface structure delineation. In this study, ground-based measurements of magnetic intensity were performed using a set of instruments in some regions of Pacitan, a city in the southern area of East Java province. Based on these measurements, data acquisition was used to identify the Grindulu faulting zone in the region of interest, potentially vulnerable to geohazards. The data were first corrected using the IGRF and diurnal corrections. A filtering technique of upward continuation at a height of 900 m was then applied to separate local anomalies from regional ones as the targeted sources in the present case. These separate anomalies and their corresponding reductions to the poles as further filtering processes were analyzed for predicting the location and direction of the fault. The results, extracted from data analysis and interpretation, show that the main path of the Grindulu is directed along the NE-SW fault line or N60oE. The resulting anomalies also reflect that the Grindulu is a normal fault with surrounding minor faults lying across the Grindulu, calling for increased awareness of vulnerability in the city to seismic threats.

Floating breakwater (PGT) is designed to be applied as a wave barrier to reduce beach abrasion and wave energy so that waves coming to the beach have their energy reduced. Compared to conventional breakwater structures, PGT structures are more advantageous if the area to be protected from impact waves has a large enough depth. This structure is more flexible because the elevation follows the tides, so this structure can be used as a wharf at the same time. It is also free from the scouring and sedimentation that often occurs on the feet of conventional breakwater structures. This study aims to attenuate and reflect waves from various PGT configurations of piling and mooring types, by testing the physical model of PGT in the wave flume laboratory of the Department of Ocean Engineering ITS, at a water depth of 80 cm, a wave height of 3.5-5.5 cm, a wave period of 0.5-2 seconds, and the angle of the mooring rope (45o, 60o, 90o). PGT is arranged in a variety of longitudinal and transverse directions to the coast. Based on the experiment, it is known that the effect of configuration and width on the PGT structure on wave transmission and reflection is influenced by the mooring angle. Configuration 3 with the largest width can give the best transmission coefficient Kt = 0.797 at 45o mooring angle and reflection coefficient Kr = 0.572 at 90o mooring angle. In type 3 fixed-configuration gives the greatest value Kt = 0.431-0.623 and Kr = 0.053-0.997 compared to other configurations. Because in configurations 1 and 2 the back of the structure is not supported by piles, so a swing occurs which generates waves. While the effect of the slope of the wave, Kt will increase as the number of waves slopes decreases, conversely the value of Kt decreases with the increase in the slope of the wave.Keywords: Floating breakwater, piling, tethered,  mooring

Pacitan is one of the cities in Indonesia which is located around a subduction zone with many faults. Grindulu Fault is one of the active faults in Pacitan. In order to mitigate hazard in the area, detailed information about the existence and characteristic of the fault is needed. Thus, imaging of Grindulu Fault using shear wave velocity (Vs) was carried out. 1-D of Vs was revealed by inversion of HVSR from microtremor data using the Monte Carlo algorithm. Furthermore, several Vs were processed using interpolation approach to determine two-dimensional (2-D) cross-section of Vs. Based on the contrast of Vs and considering the geological conditions in Pacitan area, the existence of Grindulu Fault and other faults were identified.

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