negative depths in taup velmerge

[crotwell]

merging a crustal model with negative depths (from elevation) throws error:

Error starting tool: velmerge edu.sc.seis.TauP.NoSuchLayerException: TauP Exception: VelocityModel Exception: No layer contains radius -0.3 in this velocity model.
edu.sc.seis.TauP.NoSuchLayerException: TauP Exception: VelocityModel Exception: No layer contains radius -0.3 in this velocity model.
at edu.sc.seis.TauP.VelocityModel.layerNumberBelow(VelocityModel.java:353)
at edu.sc.seis.TauP.VelocityModel.replaceLayers(VelocityModel.java:474)
at edu.sc.seis.TauP.TauP_VelocityMerge.start(TauP_VelocityMerge.java:38)
at edu.sc.seis.TauP.ToolRun.main(ToolRun.java:134)

Maybe should increase "radius of earth" to compensate, or redo layers in crustal model to make all depths positive.