Seismic Vulnerability Mapping of the Lhokseumawe Region to Support the Spatial Plan of Lhokseumawe City

Abstract

Microtremor is a weak vibration on the surface of the earth that takes place continuously due to sources of vibration such as earthquakes, human activities, industry and traffic (Daryono, 2009). Microtremor data measured obtained 3 signals whose components are vertical (Up and Down), horizontal (North-South), and horizontal (East-West) components. After the signal is obtained it can then be analyzed using the HVSR method and the dominant frequency and amplification values are obtained. The HVSR method compares the spectrum ratio of the horizontal component microtremor signal to its vertical component (Nakamura, 1989). Lhokseumawe City is administratively included in the Province of Nangroe Aceh Darussalam (NAD). In 2004 there was an earthquake of magnitude 9.2 on the Richter Scale in the southern waters of the city of Banda Aceh, which caused a devastating Tsunami. In this event many people lost about 250 thousand lives and lost property that is not small in number (Logan, 2014) Due to the active regional tectonic pattern, the NAD region is a disaster-prone region. The tectonic area of NAD is strongly influenced by the subduction area between the Indian-Australian oceanic plate (Indian Australian Plate) against the European-Asian continental plate (Eurasian plate). The tectonic pattern greatly influences the geological conditions in the waters of the study area. The purpose of this research is to provide preliminary knowledge in the use of microtremors for mapping seismic microzonation. This microzonation mapping is needed for earthquake disaster mitigation purposes, microtremor data analysis can provide information on the value of a place that is very important for earthquake resistant building planning. Building structures that have the same value as the land value will experience resonance in the event of an earthquake. Then the last is the Seismic Vulnerability Index Mapping which is useful for predicting unconsolidated sediment zones at the ground surface when an earthquake occurs, so that further studies for earthquake prone areas can be carried out. The stages of the research method carried out are measuring field data which is divided into several measurement points in each district in the city of Lhokseumawe. At each measurement point, a three-component seismometer is installed to obtain the results of the soil’s vulnerability in the area. Each measurement data is observed for 30 minutes at each point. The results of this study are the existence of areas that are very susceptible to seismic namely Ujung blang and Banda Sakti villages with seismic vulnerability index values (Kg) ranging from 0 cm/s2-30542.32 cm/s2The highest value is located at Ujong Blang villages which is 10397.1 cm/s2This is closely related to the total amount of damage to buildings in Lhokseumawe City due to the 2004 earthquake.