Simulation of Time-Lapse Microgravity in Bandung Area Using Surface and Subsurface Data
Keywords:
computation, groundwater, time-lapse microgravity, simulation, subsidenceAbstract
Utilization of excessive groundwater extraction, especially in dense urban areas can have an impact on the environment, namely the occurrence of subsidence and groundwater crisis. Non destructive monitoring using geophysics method usually applied in city area to provide information in the near surface and subsurface. The time-lapse microgravity (TLM) technique relatively simple and cheap to be conducted as monitoring method. In principle, TLM will observe changes in a gravity anomaly value at the location due to physical property in the near surface and subsurface. The conditions in the near surface and in the subsurface are considered as two main source of environmentally changes that is subsidence and groundwater level changes. In this study, a program was created to simulate TLM anomalies. The set of prism bodies are used as near surface and subsurface discretization. The program was tested using simple numerical example and then developed to accomodate real data input such as: elevation and groundwater level data in Bandung Area. We calculate the simulation of TLM in Bandung Area using data trend caused by changes in elevation using GPS geodetic survey in the period 2010-2016. We also calculate the simulation of TLM using data trend of groundwater level that occurred in 2010 until 2015. Based on the simulation in six years time-lapse, the largest subsidence produces an anomaly of about 70 μGal. Rough estimation from six years linear trend as an average estimation of one meter elevation change coresponds to TLM anomaly value of 85 μGal. The simulation results due to changes in groundwater level for five years time-lapse show the highest groundwater level rise produces an anomaly 148 μGal and the lowest groundwater level decline produces an anomaly -133 μGal.
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