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The vulnerability of land in an area to earthquake ground motions is one of the factors causing damage caused by the earthquakes. The city of Surabaya, which is crossed by two active fault segments, needs an assessment to reduce the risk of being affected by an earthquake that might occur. The aims of this study are (1) to find out the distribution of Seismic Site Classes, (20 to know the distribution of the value of Seismic Amplification, and (3) to know the potential of liquefaction in the city of Surabaya. Surabaya city, which is geologically dominated by alluvium deposits, consists of soft soil (SE) and medium (SD) sites based on N-SPT30 and Vs30 data. The level of soil amplification against earthquakes ranging from 1 to 4. This occurs because the physical properties of the Surabaya City soil layer are dominated by alluvium deposits. Regions with more than 2 amplification values are located around the coastline on the North and East coasts of Surabaya City. Based on the potential liquefaction index value, Surabaya City is included in the region with a high potential for liquefaction with a potential liquefaction index value of more than 5.

Referring to the Indonesian earthquake source and hazard map published by the National Earthquake Center (Pusgen) in 2017, it was stated that there were 34 active faults on the island of Java and could potentially be a source of earthquakes with earthquake strength more than the 6.5 M scale. Each potential source of earthquake needs to be carried out detailed research on each fault that is declared active so as to reduce uncertainty in the seismic hazard analysis. Due to limited funding and human resources researching, it is necessary to make research priorities based on the level of urgency. By utilizing decision making analysis techniques, priority of research is carried out by considering several aspects, such as the magnitude of the earthquake that may occured possible economic impact factors, population density and the level of importance of a region on a national and international scale. From the modeling results, it is shown that faults that have the potential to become earthquake sources that are located near large cities are a top priority for detailed research such as the Lembang, Semarang and Surabaya Faults.

The existence of the kendeng fault passing Surabaya is still the subject of study by the researchers after being declared active by the National Earthquake Centre. The Surabaya was passed by two segments of the Kendeng fault, the Surabaya segment and the Waru segment, the two segments had an earthquake potential of 6.5 M. In the context of disaster mitigation and earthquake analysis, more detailed information is needed relating to the geometry and position of the earthquake source with certainty, so that the identification of earthquake sources is needed in more detail. The magnetotelluric method is one of the geophysical methods that is able to properly identify anomalous objects in tens of kilometers depth. Kendeng fault as a potential earthquake source, one of its segments across Surabaya can be identified using the magnetotelluric method. Megnetolelluric measurements were carried out as many as 15 points in the Surabaya region in order to identify the geometry of the kendeng fault. From the 3D resistivity model, the inversion of magnetotelluric data can be identified well with the Kendeng fault that crosses the city of Surabaya, both the Waru segment and the Surabaya segment at a depth of less than 8 km

This research is aimed to assess the sediment transport rate under different conditions of estuary geometry by comparing the situations before and after the construction of Sembayat Weir. Sediment concentration, flow velocity, and temperature were obtained via field investigation from October 2016 to September 2017. River discharge and tidal discharge phenomenon are analyzed in the estuary, which affect hydraulic head changes. The HEC-RAS model was used for numerical modelling simulation of the hydrodynamics. The results revealed that the sediment transport rate increased under the influence of erosion in the river branches. BH2 and BH3 were the observation sites located before and after the tributary junction. Those location present the sediment transport rates decreased by 30% and 26%, respectively, in the rainy season because after weir construction. The results agree with previous research results in that sediments were deposited around the estuary weir. Meanwhile, in the river branches, a higher sediment transport rate was observed because of the tidal current that provided sediment transport over a longer term in the dry season. The findings extend the knowledge on the influence of Sembayat Weir on sediment transport rate characteristics with respect to seasonal changes. [ABSTRACT FROM AUTHOR]

The drying cycle can affect embankments based ontheir physical properties and induce soil cracks. This paper investigates the unsaturated physical behavior of material from flood embankments located at the Bengawan Solo River, Pelangwot village, Bojonegoro, East Java, Indonesia. The volumetric shrinkage and degree of compactedness of the soil are important factors that control the soil behavior due to dry conditions. Some tests were conducted to study the desiccation process, in which soil samples were placed in a circular desiccation plate with soil thickness of 10 mm and a 100 mm plate diameter. A water retention curve was obtained to analyze the material properties during shrinkage. Next, the effect of the drying process on geometric characteristics of crack patterns was analyzed by image processing. Then, photo records of cracked soil from laboratory tests were assessed to determine the soil crack intensity via a Fuzzy C-Means (FCM) method using MATLAB software. The image analysis results show that the geometric characteristics of crack patterns were influenced by the drying process with a decrease in water content at 10% intervals until the air-dried condition was achieved. This is consistent with field observations; this indicates that image processing can be used quantitatively to analyze the drying process dependency of soil cracking behavior. [ABSTRACT FROM AUTHOR]