Abstract
Local earthquake data was used to determine a three-dimensional (3D) seismic attenuation structure around the aftershock source region of the 2018 Lombok earthquake in Indonesia. The aftershocks were recorded by 13 seismic stations from August 4 to September 9, 2018. The selected data consist of 6,281 P-wave t∗ values from 914 events, which had good t∗ quality in at least four stations. Our results show that the two aftershock clusters northwest and northeast of Lombok Island have different attenuation characteristics. A low P-wave quality factor (low-Qp), low P-wave velocity (Vp), and high ratio of P-wave velocity and S-wave velocity (Vp/Vs), which coincide with a shallower earthquake (<20 km) northwest of Lombok Island, might be associated with a brittle area of basal and imbricated faults influenced by high fluid content. At the same time, the high-Qp, low Vp, and low Vp/Vs, which coincide with a deeper earthquake (>20 km) northeast of Lombok Island, might be associated with an area that lacks fluid content. The difference in fluid content between the northwest and northeast regions might be the cause of the early generation of aftershocks in the northwest area. The significant earthquake that happened on August 5, 2018, took place in a region with moderate Qp, close to the contrast of high and low-Qp and high Vp, which suggests that the earthquake started in a strong material before triggering the shallower aftershocks occurring in an area affected by fluid content. We also identified an old intrusive body on the northeast flank of the Rinjani volcano, which was characterized by a high-Qp, high-velocity, and a high Bouguer anomaly.
Highlights
Lombok Island is located in West Nusa Tenggara and is part of the Sunda Arc, Indonesia, which is controlled by the subduction of the Indo-Australian Oceanic Plate beneath the Eurasian Plate with a relative motion of 70 ± 1.0 mm/year to the north (Koulali et al, 2016)
Two major geological structures significantly control the seismicity of Lombok Island (Figure 1): the megathrust in the south due to the subduction of the Indo-Australian Plate beneath the Eurasian Plate (Hamilton, 1979) and the Flores Back-arc Thrust (FBT) north of Lombok Island which dips to the south (Hamilton, 1979; Silver et al, 1983; Irsyam et al, 2017)
For the deeper depths Miocene limestone overlain by the Pliocene to present-day young (∼ 10 km), we suggest that the low-Qp (∼ 250) is associated with a brittle area; this is based on the evidence of basal and imbricated thrust fault from the 2D seismic profile north of Lombok Island found by Yang et al (2020)
Summary
Lombok Island is located in West Nusa Tenggara and is part of the Sunda Arc, Indonesia, which is controlled by the subduction of the Indo-Australian Oceanic Plate beneath the Eurasian Plate with a relative motion of 70 ± 1.0 mm/year to the north (Koulali et al, 2016). Two major geological structures significantly control the seismicity of Lombok Island (Figure 1): the megathrust in the south due to the subduction of the Indo-Australian Plate beneath the Eurasian Plate (Hamilton, 1979) and the FBT north of Lombok Island which dips to the south (Hamilton, 1979; Silver et al, 1983; Irsyam et al, 2017). Further research conducted by Silver et al (1983) using seismic reflection data shows that this thrust extends further west to the Bali Basin
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
