ITS geologists investigate Surabaya earthquake potential

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Dr. Ir. Amien Widodo M.Si. (photo: IO/ITS)

IO, Surabaya – In response to the discovery of a fault which could po­tentially result in earth tremors and damage around the city of Surabaya, akin to the natural disasters that hit Lombok, Palu, Donggala, and most recently Situbondo, geologists from the Center for Earth, Disaster, and Climate Change of the Surabaya Su­puluh Nopember Institute of Technol­ogy (ITS) have embarked on a study of the state of the soil underneath the city. The objective of the research to attempt to mitigate the potential damage inflicted by a potential earth­quake.

Dr. Ir. Amien Widodo M.Si, an ITS Geophysics lecturer, explained that the research was based on the dis­covery of two active faults, one cross­ing beneath Surabaya and another crossing under Waru. The findings were published by the Minister for Public Works and Human Settlements (PUPR) in early September of last year. The Surabaya fault was mapped as passing Keputih to Cerme, while the Waru fault was much larger, poten­tially affecting Rungkut, Sidoarjo, Mo­jokerto, Jombang, Nganjuk, Saradan, and Cepu. “With data such as this, we can map the impact of an earth­quake resulting (from the faults),” said Amien, who is also Head of the Geo­physics Engineering and Environmen­tal Laboratory.

Other than a potentially serious effect on buildings and other struc­tures, soil conditions are also a fac­tor in understanding the dynamics of earthquakes. This is because different soil reacts differently when a tremor occurs beneath it. “Soil has its own character when hit by an earthquake: it can result in either liquefaction or amplification”.

The geological hazard expert ex­plained that liquefaction happens to sandy soil. The soil is saturated with water, and pressure from the earth­quake causes it to shift, as sand and air escape.

Soil in East and West Surabaya is mostly made up of swamp deposits, which unfortunately have a great­er potential of amplification during an earthquake. Pressure spreads through the soft soil and creates a large amplitude movement, which then rebounds from the energy of the earthquake. “In other words, its strength is multiplied”.

Compacting or condensing the soil is one possible solution to this challenge, with another being the use of pile foundations for multisto­ry buildings, as they can reduce the impact of amplification. “Many people already know that the quality of soil in Surabaya is poor; this can be seen from the large amount of backfilling preceding construction,” said the Yo­gyakarta-born man.

According to the ongoing research, there is potential for liquefaction in Surabaya, as in addition to the soil consisting largely of swamp deposits, there is also sandy soil. However, the volume of the area it affects is still unknown, as the research only scans layers. “If we continue with drilling we can see how large an area has sand and so on,” he continued. (ITS)