Infrasound and seismoacoustic signatures of the 28 September 2018 Sulawesi super-shear earthquake

Abstract

Abstract. A magnitude 7.5 earthquake occurred on 28 September 2018 at 10:02:43 UTC near the city of Palu on the Indonesian island of Sulawesi. It was a shallow, strike-slip earthquake with a rupture extending to a length of about 150 km and reaching the surface. Moreover, this earthquake was identified as one of very few events having a super-shear rupture speed. Clear and long-lasting infrasound signatures related to this event were observed by four infrasound arrays of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization as well as by one national infrasound station in Singapore. Although these infrasound stations SING (Singapore), I39PW (Palau), I07AU (Australia), I40PG (Papua New Guinea) and I30JP (Japan) are located at large distances of between 1800 and 4500 km from the earthquake's epicentral region, the observed infrasound signals associated with this event were intense, including both seismic and acoustic arrivals. A detailed study of the event-related infrasound observations and the potential infrasound generation mechanisms is presented, covering range-dependent infrasound transmission loss and propagation modeling and characterization of the atmospheric background conditions, as well as identification of the regions of seismoacoustic activity by applying a back-projection method from the infrasound receivers to potential source regions. This back projection of infrasonic arrivals allows one to estimate that the main infrasound source region for the Sulawesi earthquake is related to the extended rupture zone and the nearby topography. This estimation and a comparison to other super-shear as well as large regional earthquakes identify no clear connection between the earthquake's super-shear nature and the strong infrasound emission.

Natural and Anthropogenic Sources of Seismic, Hydroacoustic, and Infrasonic Waves: Waveforms and Spectral Characteristics (and Their Applicability for Sensor Calibration)

“…Epicentral infrasound shows frequencies in a broadband range (0.05–4.4 Hz), typically between 1 and 3 Hz (e.g. Marchetti et al 2016 ; Pilger et al 2019 ). Mutschlecner and Whitaker ( 2005 ) and Le Pichon et al ( 2003 ) observed frequencies of 0.8 Hz and 0.1 Hz.…”

“…Mutschlecner and Whitaker ( 2005 ) and Le Pichon et al ( 2003 ) observed frequencies of 0.8 Hz and 0.1 Hz. As higher frequencies are attenuated by absorption, lower frequencies are observed with increase in distance from the source (Pilger et al 2019 ). There are relations between the hypocentral depth and the frequency as well as the amplitude of the infrasonic signal (Mutschlecner and Whitaker, 2005 ).…”

Infrasonic Earthquake Detectability Investigated in Southern Part of Japan, 2019

“…Not likely, in the earthquakes which are generated from strike-slip fault mechanism, no P-waves were detected by infrasound sensor as shown in Figure 5 , for sensors very close to the epicentral locations in the cases of 11 and 13 of March 2019. As the signals from near infrasound sensor did not well-correlated in time and frequency domain, moreover, among many studies applied on the generation of infrasound from earthquakes, only a few of them reported with a super shear-rupture speed [ 15 ]. According to Shelly et al (2008) [ 16 ] Shikoku Island is characterized by low-frequency earthquakes and thus, one possibility that the tremor results from a slow shear slip.…”

Audible acoustics from low-magnitude fluid-induced earthquakes in Finland

“…The event magnitudes associated with these sounds have been stated to be as low as -2 and -0.7, respectively. Audible noises are also frequently reported for larger magnitude earthquakes, and accompanied by the frequent detection of infrasonic acoustic waves at global distances [6][7][8][9][10][11][12][13][14] . Mapping of acoustic sources during and immediately after earthquakes has identified three sources of earthquake acoustic signals 15 : i) 'epicentral' (i.e.…”