The B-Value determination of the ambarawa earthquake swarm from 22 October, 2021 to 9 November, 2021 using the least squares method
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Author |
Anisatul Millah and Gatot Yuliyanto
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e-ISSN |
1819-6608 |
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On Pages
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1094-1101
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Volume No. |
20
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Issue No. |
14
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Issue Date |
October 31, 2025
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DOI |
https://doi.org/10.59018/0725126
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Keywords |
b-value, a-value, earthquake swarm, least square method, magnitude of completeness.
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Abstract
The earthquake swarm that occurred in Ambarawa, Central Java, from 23 October 2021 to 5 November 2021 recorded 42 earthquakes with a magnitude of less than 5 and were at shallow depths. Even though the earthquake shaking did not cause damage to strong buildings, the community could feel the shaking on II-III MMI. Ambarawa is flanked by 4 active faults, namely the Ungaran-1 fault in the north, the Ungaran-2 fault in the north, the Merapi-Merbabu fault in the south, and the Baribis-Kendeng Fold Thrust Zone in the east. Determination of the b-value is carried out to determine the level of stress and heterogeneity in the crust of Ambarawa, and the determination of the a-value is carried out to determine the frequency of earthquakes that occur in Ambarawa. The method used is the Least Squares Method (LSM) concerning the Gutenberg-Richter Law and using earthquake data with magnitudes above Mc (Magnitude of Completeness). The b-value obtained is 1.6 ± 0.15, which indicates that Ambarawa has a crust with low stress and high heterogeneity. The a-value obtained is 5.8, which indicates a high level of seismic frequency in Ambarawa, so that the earthquake return period is short.
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