Development of the Groundwater Level Changes Detector for Earthquake Prediction at Yogyakarta Region – IndonesiaHerlambang Laksamana Firdaus, Sunarno, Memory Motivanisman Waruwu and Rony WijayaMATEC Web Conf., 218 (2018) 02010DOI: https://doi.org/10.1051/matecconf/201821802010