Analysis of split normal modes for the 1977 Indonesian earthquake

Abstract
The longest period spheroidal mode multiplets, 0S2 to 0S5, are well recorded on IDA gravimeter records of the 19 August 1977 (Ms734) Indonesian earthquake. We model these modes, which are split into singlets by rotation and ellipticity, using time domain synthetics which reproduce the complex interference pattern between the various singlets in each multiplet. This method, developed to fit a single strainmeter record of the Chilean earthquake, successfully fits records at multiple stations using a common source. We also study the attenuation of the split modes by matching the decay of multiplet envelopes and individual singlets.