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Appropriate Seismic Risk for Earthen Dam

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Please consider the following: Earthen dam, circa 1920's and 1940's construction (phase 1, then heightened in phase 2), currently Zone 3.  Slope stability on downstream face was analyzed for 10%/50 year event and found to be 1.0.
This dam impounds drinking water for a moderately sized community (70,000+), with the treatment plant immediately below.  High population densities are somewhat removed, however.  It seems to me, given the potential results of failure that this structure should be evaluated more stringently than just any old office building...say 2%/50 year OR set the performance level to "Immediate Occupancy" at 10%/50 year.
Anyone out there have an enlightened opinion regarding input ground motion?
Regarding the virus:  With an opening line of "I love you" it obviously wasn't aimed at structural engineers.  Now, if it had a subject line of "LRFD vs ASD" we'd still be cleaning up the mess....
Thanks for any ideas - you are welcome to email me directly at loeth(--nospam--at) if you feel discretion is warranted.
Larry Oeth PE