On December 6, 2016, an Mw 6.5 earthquake occurred in Pidie Jaya, Aceh, about 30 km to the north of Sumatran Fault (SF) that killed more than 100 people ManuscriptClick here to download Manuscript SRL_Muzli_etal_Manuscript_revised2.docx

Seismic swarms close to volcanoes often signal the onset of unrest. Establishing whether magma is the culprit and the unrest can be flagged as magmatic may be challenging. Here we analyze the spatio-temporal pattern of a seismic swarm that occurred in November 2015-February 2016 around Jailolo volcano, a long-dormant and poorly studied volcano located on Halmahera island, North Moluccas, Indonesia. The swarm included four M w > 5 earthquakes and hundreds of events were felt by the population. We relocate the earthquakes using both the Indonesian Seismic Network and singlestation location techniques. We find that the earthquakes cluster in a narrow strip, stretching 5 km E-W and 20 km N-S, migrating southward away from Jailolo volcano at ∼10 km/d. We investigate the source mechanisms of the largest earthquakes via full moment tensor inversion. The non-double-couple component is around 50%, such that the earthquakes, besides normal faulting, included a relatively large opening component. After a thorough examination of the possible causes of the Jailolo swarm we conclude that a laterally propagating dike of tens of millions of cubic meters is the triggering mechanism for the seismicity. The swarm marks the first documented magmatic unrest at Jailolo. We find that there is a probability >0.1 that the unrest will last for more than 2 years. This magmatic unrest calls for the classification of Jailolo volcano as active, and for an urgent assessment of the associated volcanic hazard.

No abstract

ABSTRAKVariasi nila-b dari relasi Gutenberg-Richter memegang peranan penting dalam sebagian besar model prakiraan gempabumi yang terkait dengan resiko bencana. Dari relasi Gutenberg-Richter yaitu log N = a -bM, slope dari hukum pangkat ini merupakan nilai-b yaitu sebuah paremeter tektonik yang menggambarkan ukuran distribusi dari gempabumi. Nilai-b yang tinggi mengindikasikan suatu proporsional yang relatif besar dari gempa-gempa kecil dan nilai-b yang rendah sebaliknya. Di dalam analisis kegempaan ini, kelengkapan katalog gempabumi merupakan faktor penting yang dapat mereduksi timbulnya deviasi linearitas. Katalog gempabumi NEIC dari tahun 1973-2006 dan katalog gempabumi BMG digunakan untuk analisis variasi nilai-a, nilai-b dan periode ulang gempabumi di Zona Subduksi Jawa dengan batas 6,5° LS -12° LS dan 105° BT -115° BT. Dari analisis katalog gempabumi di wilayah penelitian diperoleh variasi nilai-b berkisar antara 0,8-2,5, variasi nilai-a berkisar antara 6-12 sedangkan periode ulang gempabumi dengan magnitude 6 secara umum adalah sekitar 5 tahun.

Lombok and Nusa Tenggara are one of the regions in Indonesia that have quite complex tectonic arrangements. With this order, not infrequently in the region there are often natural disaster phenomena. One of the most striking things is the occurrence of a series of earthquakes of magnitude Mw > 5.0 that rocked the northern region of the Island of Lombok on 29 July 2018 (Mw = 6.4), 5 August 2018 (Mw = 6.9), 9 August 2018 (Mw = 5.9), 19 August 2018 (Mw = 6.3 and 6.9) and 25 August 2018 (Mw = 5.5). This study aims to identify the condition of tectonic structures under the surface of the earthquake occurring region using the tomography method. This method utilizes earthquake travel time data recorded at 15 BMKG seismic stations. The tomogram results show the contrast of anomalous values in the Vp and Vs models. The contrast of the anomalous is associated with the presence of fault structures that have an allowance angle of about ± 20-30° and a thrust fault type, verified by focal mechanism ball data. This thrust fault is then indicated as the cause of the occurrence of earthquakes with magnitude Mw > 5.0, which shook the northern part of the island of Lombok in July-August 2018. According to the tomography result, the fault is located closer to the north side of Lombok Island than Flores Back arc Thrust.