RECONSTRUCTION OF RAYLEIGH WAVE GROUP VELOCITY MAP BENEATH âNDHâ GEOTHERMAL FIELD USING AMBIENT SEISIMC TOMOGRAPHY
Ambient seismic noise, that can be caused by human and/or environmental activities, actually contains similar subsurface information as the seismic waves generated from artificial energy sources or earthquake. Compared to other seismic waves, ambient noise containt more continous informations as it...
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| Format: | Final Project |
| Language: | Indonesia |
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| Online Access: | https://digilib.itb.ac.id/gdl/view/32355 |
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| Institution: | Institut Teknologi Bandung |
| Language: | Indonesia |
| Summary: | Ambient seismic noise, that can be caused by human and/or environmental activities, actually contains similar subsurface information as the seismic waves generated from artificial energy sources or earthquake. Compared to other seismic waves, ambient noise containt more continous informations as it constantly travels through the Earth. In this study ambient seismic noise tomography (ANT) was applied to image the subsurface image beneath the “NDH” geothermal field. Data was collected from local seismic network of 8 months recordings (January-July and September-October 2016). This study apply the cross correlation based ambient noise interferometry to infer the subsurface description from lateral variation of group velocity maps as a function of frequencies. The ambient noise interferometry utilize the dispersive signals that emerge on emphirical Green’s function obtained from cross-correlation operation between seismogram of all station pairs, which reflects seismic velocity structure beneath the surface. The emphirical Green’s function is used to extract Rayleigh wave kurva dispersi s, by applying Multiple Filtering Technique, one of the Frequency-Time Analysis method. The measurements of group velocity between station pairs in several periods, are used to construct Rayleigh wave group velocity maps by ambient noise tomographic inversion. Surface waves tomography produce Rayleigh waves group velocity maps for periods 1 – 8 s. This group velocity maps resolve high group velocity zone in western part Gunung Gambung shown that related with heat sources system of “NDH” geothermal filed whereas low group velocity zone is correlated with heat manifestation such as hot springs and fumarole. The existence of low velocity zone is associated with volcanic formation, and high-low velocity transition zone around Gunung Wayang as a weak zone and fluid migration. |
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