Seismic source mechanisms of tremor recorded on Arenal volcano, Costa Rica, retrieved by waveform inversion

International audienceMoment tensor inversions of volcanic tremor are synthetically tested and subsequently applied to a dataset recorded on Arenal volcano in 2005. We selected 15 harmonic tremor events showing an emergent but very clear onset with a fundamental frequency range of 0.8-1.5 Hz. These events constitute an excellent opportunity to broaden our knowledge of tremor generation models. The inversions were performed for a common source location, the position of which was retrieved through the evaluation of the joint probability density function of the misfit values obtained by the moment tensor inversion of all the events and all predefined source locations (grid search). Events are located beneath the summit crater, in a shallow position. The inversion procedure was tested through the use of synthetic tremor, generated using full wavefield numerical simulations. The maximum amplitude decomposition method is used to analyse the solutions of the synthetic tests. The results highlight the stability of the moment tensor solution when the whole length of the signal is used in the inversion procedure. Hence the whole length of the tremor is utilised to retrieve the source mechanism generating the 15 tremor events. A sliding window is utilised to investigate the time variability of our solution. A crack dipping 20° to the North-Northeast is reconcilable with all 15 tremor events. This mechanism is found to be constant for the entire length of each tremor and for different events

Estimasi Mekanisme Sumber Gempa Low Frequency Menggunakan Waveform Inversion Pada Gunungapi Papandayan

Gempa Low Frequency (LF) telah terekam pada Gunungapi Papandayan dalam rentang waktu Bulan September 2015 dengan frekuensi maksimum kurang dari 5 Hz. Distribusi episenter dari LF tersebar di Kawah Mas dan Kawah Nangklak dengan kedalaman terbagi kedalam dua kelompok, yaitu 0.7 sampai 2 km dan 5 sampai 6 km. Momen tensor dari Gempa LF didapatkan dari inversi waveform dengan melihat korelasi waveform data dengan waveform sintetik dengan beberapa aspek yaitu, korelasi terhadap kedalaman centroid, time shift, presentase DC dan fitting waveform. Dari keenam gempa yang dianalisa, dua gempa mempunyai presentase DC yang lebih dominan 63% dan 66% dengan solusi bidang patahannya adalah strike-slip dan oblique-reverse. Dan untuk gempa yang lain, mempunyai presentase non-DC yang lebih dominan 55% sampai 85% dengan solusi bidang patahannya strike-slip, normal, reverse dan dip-slip. Gempa LF berasosiasi dengan sistem hidrotermal dengan mekanisme sumber diakibatkan oleh rekahan pada dinding-dinding resevoir hidrotermal karena adanya tekanan dan pengisian fluida pada rekahan tersebut secara cepat. Selain itu, pada bagian pipa konduit, membentuk rekahan sub-vertikal dari pipa yang terisi fluida ========================================================================================================= Low Frequency (LF) events has been recorded on Papandayan Volcano in September 2015 with a maximum frequency of less than 5 Hz. The distribution of epicenters of LF beneath Mas crater and Nangklak crater with depth divided into two groups, 0.7 to 2 km and 5 to 6 km. Moment tensor of LF event obtained from waveform inversion by using waveform correlation with synthetic waveform and other aspects, specifically, correlation of the centroid depth, time shift, the percentage of DC and fittings waveform. From six events were analyzed, two events have dominant DC percentage 63% and 66% with a faultplane solution are strike-slip and oblique-reverse , And for another events, the percentage of non-DC has a dominant 55% to 85% with the faultplane solution are strike-slip faults, normal, reverse and dip-slip. LF event associated with the hydrothermal system and the source mechanism generated by fractures in the walls of the hydrothermal reservoir with the pressure of fluid-filled in fracture rapidly. In pipe conduit, forming cracks in sub-vertical of the pipe also generate LF event