Geoelectric and microtremor are geophysical methods that can be used to determine subsurface conditions, especially in determining the presence of aquifer zones. This study aims to determine the potential and presence of aquifer rocks in the Grabag District area through microtremor and geoelectric methods and to compare the results of the two methods. The area of the Grabag District is very limited in conducting geoelectrical research because it is related to narrow topographical contours, so a microtremor method is needed to determine the condition of the aquifer below the ground surface. Measurements in this study resulted in 3 geoelectric trajectories and 20 microtremor measurement stations. The results of microtremor and geoelectric measurements have a good correlation between the two. The geoelectrical method uses resistivity parameters while the HVSR method uses v_s and Poisson’s ratio parameters. There are several anomalies that can be suspected as the presence of aquifer zones such as surface water found at station 2, unpressured aquifers at stations 16 and 19, depressed aquifers at stations 1, 10 and 20 and water loss zones at stations 4, 2 and 13. Based on the advantages of the two methods in collecting data in the field, microtremor is more flexible and better used in narrower conditions like in this study and the depth of microtremor does not depend on how long the stretch is like geoelectric.

Keywords: microtremor, geoelectric, resistivity, HVSR, aquifer zone, Poisson’s ratio, Grabang Magelang

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