Pesawaran, Lampung telah diguncang rentetan gempa bumi magnitudo rendah pada bulan Januari 2021. Gempa bumi tersebut tidak disertai dengan gempa utama dengan magnitudo besar sehingga dapat disebut dengan gempa swarm. Relokasi hiposenter telah dilakukan dengan mengunakan data dari jaringan stasiun BMKG untuk mengetahui sumber dari gempa swarm tersebut. Metode double-difference digunakan dan didapatkan hasil relokasi 19 dari 22 gempa swarm yang terjadi. Distribusi kedalaman hiposenter berkisar pada kedalaman 1,5-4,5 km sehingga dapat disebut dengan gempa kerak dangkal. Berdasarkan sayatan melintang terhadap kedalaman teramati bahwa sebaran gempa memiliki kemiringan ke arah Timur Laut. Lokasi gempa yang presisi juga menunjukan bahwa adanya deliniasi dan tepat berada di atas terduga Sesar Menanga. Berdasarkan analisis hasil relokasi hiposenter dapat disimpulkan bahwa gempa swarm Pesawaran disebabkan oleh aktivitas Sesar Menanga.

The Mw 7.5 Palu earthquake that occurred in Palu-Central Sulawesi, Indonesia, on September 28, 2018, accompanied by the tsunami and liquefaction caused casualties and building damage in the city of Palu and its surroundings. One month later, a series of earthquakes swarm occurred in Mamasa, West Sulawesi. In this study, coulomb stress were calculated using a half-space elastic model in a square plane which is assumed to be homogeneous isotropy to analyze whether there is a relationship between earthquakes that occur in Palu and earthquakes swam in the coulomb stress field changes. The results show that the area that experienced a stress reduction predominantly towards the north and south of the mainshock hypocenter, while the aftershocks were at an increase in coulomb stress changes, so that the Mamasa earthquakes swarm probably have been triggered by the Palu earthquake.

We present here an analysis of the destructive Mw 6.2 earthquake sequence that took place on 14 January 2021 in Mamuju–Majene, West Sulawesi, Indonesia. Our relocated foreshocks, mainshock, and aftershocks and their focal mechanisms show that they occurred on two different fault planes, in which the foreshock perturbed the stress state of a nearby fault segment, causing the fault plane to subsequently rupture. The mainshock had relatively few aftershocks, an observation that is likely related to the kinematics of the fault rupture, which is relatively small in size and of short duration, thus indicating a high stress-drop earthquake rupture. The Coulomb stress change shows that areas to the northwest and southeast of the mainshock have increased stress, consistent with the observation that most aftershocks are in the northwest.

Sorik Marapi is an active volcanic mountain with an altitude of 2,145 meters located in Batang Gadis National Park, Sibanggor Julu Village, Mandailing Natal Regency, North Sumatra, Indonesia. Since the earthquake in Aceh on December 26, 2004, geological conditions in the western part of Sumatra Island have increased in stress. This affects the volcano in Sumatra, Mount Sorik Marapi, so it needs to be studied to find out the condition of changes in coulomb stress in Sorik Marapi. The method used in this study is a descriptive method with an analysis of the coulomb stress method. From the Aceh earthquake year of December 2004 to 2021, Mount Sorik Marapi experienced the highest average increase in coulomb stress in 2012, which was 0.171 bars. The highest average increase in shear in 2015 was 0.25 bars, and the highest average normal increase in 2018 was 0.202 bars. While at depth, Sorik Marapi mountain experienced an average change in coulomb stress highest of 0.368 bars, the average increase in the highest shear by 0.269 bars, and the average normal increase of 0.246 bars. All such increases are at a depth of 90 km below sea level. Based on the results of this study, it is stated that Mount Sorik Marapi experiences inconsistent changes in coulomb stress every year.

On February 25, 2022, the Mw6.2 “Pasaman Earthquake” took place in central-west Sumatra in association with activity in the Sumatran Fault system. This study clarifies the spatial and temporal distribution of the Pasaman Earthquake sequence and forecasts the earthquake sequence’s impact on the seismicity in the vicinity and in the Sumatran Fault system. We first examined the seismicity before the mainshock and observed significant low b-value anomalies both in time and space, shedding light on the earthquake precursor by monitoring b-values prior to the event. Based on the first 18-day aftershocks, we modelled the temporal distribution of the mainshock according to the modified Omori’s law, which suggested this sequence could last 37 or 451 days. To understand the spatial pattern of the aftershocks, we calculated the coseismic Coulomb stress change imparted by the Pasaman Earthquake mainshock. The stress increase extended northwest and southeast, consistent with aftershock distribution. We further evaluated rupture probability for each segment of the Sumatran Fault. Considering the stress perturbation imparted by the Pasaman Earthquake, we expected a seismicity rate increase of ca. 40% at the Sumpur and Sianok segments in the short term. To quantify long-term rupture probability, the recurrence interval and the time elapsed since the previous earthquake were incorporated based on the time-dependent Brownian Passage Time (BPT) model. A high rupture probability is expected for a segment with a short recurrence interval and/or long time elapsed since the last earthquake. The earthquake probability at the Sumani segment in the coming 50 years was determined to be 72.0%. The outcomes of this study are the be-all and end-all for subsequent probabilistic seismic hazard assessment for not only Sumatra, but also certain metropolises in Malaysia and Singapore.