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Jakarta Post

A constant threat of earthquakes in Aceh

  • Syamsidik and Ibnu Rusydy

    The Jakarta Post

Banda Aceh, Aceh   /   Wed, July 10, 2013   /  11:04 am

The earthquake that shook Aceh on July 2, was a recent reminder for all of us of the level of vulnerability of the province to the geological hazard. The central part of Aceh is transected by a well-known Sumatran Fault Zone (SFZ) that bisects Sumatra just around the middle of the island.

According to the US Geological Survey (USGS), the Sumatran Fault is classified as a major transformed structure that moves 10-27 millimeter per year.

However, some areas along the transects, especially around Aceh province, have been anticipated by many geologists as among the most probable seismic gaps on land as they have not moved for more than a century.

Since 1892, no land earthquakes with a magnitude larger than 6.0 were recorded. Three earthquakes occurred on July 2 (magnitudes 6.2, 5.3 and 5.1) that indicate lateral movements of the segment along the Sumatran Fault.

Although the quakes are classified as medium in terms of magnitude, they were deadly due to the shallowness of their epicenters. The shallow earthquake with a magnitude of 6.2 amplified its energy to the surface soil layer around the epicenter that resulted in massive damage to the buildings and infrastructure around the affected area.

Central Aceh regency is dominated by thick volcanic sediment that can amplify the deep earth crust force to an extremely large one on the surface. This can potentially destroy most of the constructions built around the area. This explains why numerous buildings were flattened by the earthquake.

Geologists and other scientists had warned people and local governments that a major earthquake was likely to occur anytime.

Confusion and anxiety occupied the people'€™s minds around Bener Meriah regency due to unclear information that the earthquakes were triggered by Burni Telong volcano activities.

People feared that the volcano eruption would follow as a result of the magmatic movement. There was not much information available for the ordinary people whether the assumption was true or otherwise. Although clarification was made, the information barely reached the community at the early period of the event.

The difference between a volcanic earthquake and tectonic earthquake can be distinguished based on the damage caused and based on seismic-volcano monitoring results. The former is rather easy to understand by the people.

A volcano eruption should have preliminary indications such as small temblors, smoke and gas released from the volcano'€™s crater and sometimes an animal'€™s unusual behavior can be an indication.

Yet, the understanding was not available among the people. Mass evacuation and panic were seen as a result of the confusing information.

Information about the hazard had reached key parts of the community and government officials of the area. Before the July 2 earthquake, an earthquake of magnitude 5.0 that occurred in August 2009 was a clear warning. The 2009 quake, although it claimed no lives, caused public infrastructure and people'€™s houses to collapse.

At that time, a briefing to key persons in Aceh about the threat was delivered. It was expected that the related stakeholders would take concrete steps toward creating a resilient region.

Our team found that combinations of the earthquakes force and the poor quality of the buildings in the region contributed to the amount of damage in 2009. Since that time, there have been no significant improvements observed on building codes and quality control of the buildings themselves.

The most recent earthquake was stark evidence of the deadly combination between the hazard and a lack of preparedness for the earthquake that caused severe damage and a number of casualties.

Learning from the sequence of earthquakes, questions concerning actions made could be raised. Why was the real threat of the earthquake mostly dismissed? How should the information be delivered to make important changes in the community and in regulation enforcement on making the region disaster-resilient?

Disaster Risk Reduction (DRR) outreaches at districts located around Mount Bukit Barisan in Aceh province are less familiar than at other districts that were affected by the 2004 tsunami. Since 2005 until recently, many DRR programs focused on enhancing community and region capacity toward tsunamis and floods.

Less attention has been paid to earthquakes and to the central region in Aceh. This contributes to making the community less aware due to the mode of communication used in disaster risk reduction campaigns. Although relevant information had been given to policy makers in the region, the information campaign might not have reached communities directly exposed to the disasters.

On the other hand, although there was direct information on earthquake risk reduction, communication was limited in its reach due to the limited ways used to inform the community.

Also, people in the central region use locally available construction materials to build their houses. According to civil engineering guidelines, mortar should contain a specific grade of material.

However, sites to quarry the material are difficult to find around the regency due to its difficult terrain. The people use poorly graded material that is loose and results in less solid and compact building
structural elements.

The use of light concrete material has been promoted but has attracted little attention from people to replace conventional heavy concrete material with the light one. Light concrete can sustain earthquake tremors better than the heavy one. Conventional building materials such as bricks and other heavy materials have long been used by the community. People are reluctant to adopt the new concept of constructing houses with newly developed light material.

Further analysis on the regional spatial planning revealed that, although it contains disaster mitigation principles, not much detail of the building-construction regulation has been made to enforce earthquake-resilient construction.

Threats of the SFZ still exist and are constant. A large seismic gap still lies from the central region of Aceh to the northern area up to Banda Aceh city. Millions of people live in this area and trillions of rupiah worth of infrastructure have been built. It is sadly true that the seismic gaps exist and there is the potential for a major disaster.

All regional and city development regulations and systems regarding monitoring and supervising development should be reviewed thoroughly in order to save Aceh and its people.

Syamsidik is head of applied research division at the Tsunami and Disaster Mitigation Research Center (TDMRC) and lecture at civil engineering department of Syiah Kuala University in Banda Aceh. Ibnu Rusydy is a geo-hazard researcher at TDMRC and a lecturer at geo-physics engineering department of Syiah Kuala University.

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