The research result of Earthquake and Landslide Study Team from Geological Engineering of UGM recommended creatingÂ the mapping of potential earthquake and landslide hazard zoneÂ in West Sumatra. This is very helpful for early rescue of more people and for support improvement of spatial and regional development in future reconstruction.
"Mapping of earthquake and landslide hazard zone is needed as a direction for spatial refinement and regulation of new building in reconstruction phase, as once conducted in Yogyakarta and Bantul regency," said Chairman of the Earthquake and Landslide Study Team, Prof. Dr. Dwikorita Karnawati, Thursday (8 / 10), at Parahita Stana Room, UGM central office.
According to Dwikorita, another important result of observations on geological conditions after the earthquake in Padang, Pariaman, SolokÂ and Padang Panjang is the possibility of landslides which are still potentially to occur if triggered by heavy rains or aftershocks. The observation was also conducted to assess geological conditions that affect the level of building damage and soil erosion due to the earthquake. From the results of observation and measurement in the field, it is known that the region affected by the earthquake in West Sumatra on September 30 can be divided into two main areas: alluvial plains and hard areas of the hill.
Alluvial plains include Padang,Â Pariaman and Padang Panjang which suffer much buildings damage because of the earthquake. This region is composed of loose sediments in the form of clay, sandy clay, and gravel sand. When an earthquake happened, earthquake wave vibration was experiencing complications and became surface spread,Â swinging both vertically and horizontally, which ultimately caused buildings to damage and collapse.
"Most of buildings have collapsed or swayed toward the northwest-southeast, to the earthquake epicenter at the northwest of Padang city," she said.
Unlike the impact of the earthquake in Yogyakarta, said Dwikorita, the damage that occurred on alluvial plains in the valley does not show a specific pattern of distribution controlled by soil conditions or geological conditions, it seemed that it is more controlled by the condition of building construction.
Meanwhile, hard areas of the hills including the Bukit Barisan area from Padang Panjang to Solok experienced many landslides. According to Dwikorita, the hills are composed of volcanic igneous and metamorphic rocks, and they are the hills formed by active faults known as Semangko fault.
"In the fault zone, rocks forming these hills are also broken by rock cracks and they are fragile. Consequently, when shaken by earthquakes, much debris occurred on Barisan hillsides, especially those on the fault lines, " she explained.
Several landslides had buried more than 100 people in two villages: Kapalo Koto and Lubuk Lawe in Cumanak village, Nagari Tandikek, Patamuan sub-district, Padang Pariaman regency. The landslides on the rocky slope were estimated to be on the fault lines. The degree of the slope ranges from 30 to 40 degrees.
"The soil condition in the fault zone is very fragile and still has the landslide potentials if an earthquake occurs, or washed by heavy rains. We recommend the closure of this zone when it rains to avoid casualties," she suggested.