B-VALUE’S ANALYSIS BEFORE AND AFTER LOMBOK EARTHQUAKE 2018

• Main Author: Ilyas Bashirah Putra Arya, Moh.
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/47301
• Institution: Institut Teknologi Bandung

During period less in a month, Lombok has experienced earthquakes with magnitude M > 6, which specifically happened on 28th July 2018 (6,4 M), 5th August 2018 (6,5 M), and 19th August 2018 (6,3 M and 6,9 M). All of the earthquake's hypocenter located in the north of Lombok island at the shallow depth (< 30 kilometers). Variety of earthquake’s distribution explained by the bvalue in Gutenberg-Richter equation using the Maximum Likelihood approachment. b-value is calculated using the earthquake's catalog from BMKG that has relocated by PuSGeN in 1 Oktober 2009 until 31 November 2018 period which limited by the location of hypocenter and the similarity of earthquake's focal mechanism in the Lombok region. The processing of the earthquake's catalog is utilized by ZMAP 6.0 software with sampling window size that varies from 20, 30, 40, and 70 in order to gain the most optimum b-value's model. The bvalue's result is analyzed on each 2018 Lombok earthquake events using "b-value vs time (2009 - 2018 period)" graphic model and "b-value vs time (2018 period)" model graphic, in which the constriction of b-value that recorded is observed before the main events happened. The b-value's result is also analyzed on 2018 Lombok's earthquake sequence using "b-value vs time (2009 - 2018 period)", in which the decreasing of b-value statistic is observed before the main events happened and the b-value's trend after the main events is couldn't be considered because the minimum data that needed is not fulfilled. The decreasing of b-value before the 2018 Lombok's earthquake sequence may indicate the accumulation of stress concentration which caused the fault plane activation in northern Lombok island. However, the correlation between the statistic decreased of b'value with stress concentration and another physical parameter required more research