Technical Cooperation Project Georisk Indonesia - Microzonation

Report of the project:

• Indonesia - Good local Governance – Mitigation of Georisks
• Indonesien - Gute lokale Regierungsführung - Verminderung von Georisiken

Indonesia’s geotectonic setting on or close to major tectonic plate boundaries is the reason for a very high earthquake hazard, which affects almost the entire country. Consequently, the history of destructive earthquake events is long and the death toll is very high.

Seismic microzonation maps outline zones of different earthquake hazard potentials at an urban scale. Microzonation requires large-scale mapping of the distribution of soft soils and their physical properties using geological, geotechnical and geophysical methods as local geological conditions strongly influence the intensity of ground shaking during an earthquake.

In a time of fast and often uncontrolled urban settlement growth, large-scale mapping becomes indispensable for a sustainable urban development planning, where classical seismic hazard mapping PSHA (Probabilistic Seismic Hazard Assessment) is not providing the necessary resolution regarding local subsurface site conditions.

In Indonesia, almost all major cities are situated in earthquake prone regions, while they face the highest rates of urbanization. In order to strengthen GAI’s (Geological Agency of Indonesia) capacities on this matter, the Georisk Project abets the development of a best-practice workflow of methodologies to produce microzonation maps, adapted to Indonesian conditions through training of technical staff from the researcher division of GAI and extensive field measurements. In a further step, Georisk-Project masses on the effective implementation of microzonation studies on local level complying with the national building code and spatial planning regulations.

As there are currently various actors in Indonesia conducting microzonation studies, applying different methodologies, Georisk-Project supports the formulation of an Indonesian Standard on microzonation and a guideline in order to harmonize the results and assure the quality of the latter.

Activities

In its final phase the Georisk-Project introduced capacity building activities in the field of microzonation in order to strengthen capacities of GAI for carrying out microzonation studies. Since there is no standard procedure to produce microzonation maps, the aim is to develop a best-practice work flow of methodologies adapted to Indonesian conditions. An expert installed in the Georisk team in 2012 is working on this subject together with colleagues from PSG (Centre for Geological Survey, department within GAI).

Several training courses have since been conducted, covering the application of special geophysical methods that are most relevant for microzonation studies, in particular ambient vibration (seismic noise) techniques for site characterization (Figure 1). The courses, held by international experts, were attended by participants from GAI and Indonesian Universities and were partly accompanied by training-on-the-job activities. Furthermore, the equipment available at GAI for ambient vibration measurements was upgraded by purchase of two modern seismic recorders and seismometers (Figure 2).

The City of Mataram on Lombok Island (Indonesia) is the pilot area for the development of a strategy to implement microzonation studies most effectively and complying with national building code regulations. During a field campaign in 2013, ambient vibration (seismic noise) measurements were carried out at several hundred sites in the city (Figure 3). Data processing was done using software developed by the Georisk-Project (Figure 4).

The results of the measurements reveal detailed information on the distribution and physical properties of soft sediments in the subsurface of the city which is crucial for estimating the intensity of shaking at different sites during an earthquake. A final microzonation map based on this data outlines relative seismic hazard zones on municipal level (Figure 5). This map can help city planners in geo-hazard sensitive urban development. The effective implementation of microzonation data in local government decision-making processes is the final aim of the Georisk-Project microzonation activities. The concept of microzonation developed for communities in Indonesia is outlined in Ibs-von Seht (2014): Microzonation Studies using Microtremor. Manual (PDF, 14 MB).

Fig. 5: Microzonation map of Mataram City (Lombok, Indonesia) indicating zones of relative seismic hazard on municipal level (blue=lowest, orange=highest). The map is based on seismic (ambient vibration, seismic noise) data taken at about 500 sites in the city Source: BGR

For more information you can download the Project Brochure here.