removed backbone log-lin-log conversion

src/main/java/gov/usgs/earthquake/nshmp/gmm/UsgsPrviBackbone2025.java

@@ -29,8 +29,6 @@ import static gov.usgs.earthquake.nshmp.gmm.GroundMotions.EPI_IDS;
 import static gov.usgs.earthquake.nshmp.gmm.GroundMotions.EPI_WTS;
 import static gov.usgs.earthquake.nshmp.gmm.SubductionZone.Type.INTERFACE;
 import static gov.usgs.earthquake.nshmp.gmm.SubductionZone.Type.SLAB;
-import static java.lang.Math.exp;
-import static java.lang.Math.log;
 import static java.lang.Math.sqrt;
 
 import java.util.Map;
@@ -178,10 +176,10 @@ public abstract class UsgsPrviBackbone2025 implements GroundMotionModel {
       GroundMotion gm = (gmTree.size() == 1)
           ? gmTree.get(0).value()
           : gmTree.get(1).value();
-      median += exp(gm.mean()) * b.weight();
+      median += gm.mean() * b.weight();
       sigmaSq += gm.sigma() * gm.sigma() * b.weight();
     }
-    return GroundMotion.create(log(median), sqrt(sigmaSq));
+    return GroundMotion.create(median, sqrt(sigmaSq));
 
   }