diff --git a/src/main/java/gov/usgs/earthquake/nshmp/calc/CalcConfig.java b/src/main/java/gov/usgs/earthquake/nshmp/calc/CalcConfig.java
index 39e0b3e1a85ba1b1d23eb9d96f52597950641143..7ec631bf64bdfeee00cdf4741225004daa35db5a 100644
--- a/src/main/java/gov/usgs/earthquake/nshmp/calc/CalcConfig.java
+++ b/src/main/java/gov/usgs/earthquake/nshmp/calc/CalcConfig.java
@@ -32,6 +32,7 @@ import java.util.Set;
 import java.util.TreeMap;
 
 import com.google.common.collect.Maps;
+import com.google.common.collect.Range;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonDeserializationContext;
@@ -213,8 +214,8 @@ public final class CalcConfig {
      * will apply a damping scale factor (DSF) to adjust the 5% damped spectral
      * ordinates predicted by GMMs.
      *
-     * <p><b>Default:</b> {@code 0.05} (5.0%)<br><b>Range:</b> {@code 0.5%} to
-     * {@code 30.0%} (0.005 to 0.3)
+     * <p><b>Default:</b> {@code 0.05} (5.0%)<br><b>Range:</b> {@code 0.005} to
+     * {@code 0.3} (0.5% to 30.0%)
      *
      * <p><b>Note:</b> At this time, the damping scaling factor (DSF) model
      * (Rezaeian et al., 2014) is only applicable to active continental crust
@@ -225,6 +226,15 @@ public final class CalcConfig {
      */
     public final double gmmDampingRatio;
 
+    /**
+     * Factor by which the aleatory variability (sigma) for all GMMs should be
+     * scaled.
+     *
+     * <p><b>Default:</b> 1.0<br><b>Range:</b> {@code 0.5} to {@code 1.0} (50%
+     * to 100%, no scaling)
+     */
+    public final double gmmSigmaScaling;
+
     /**
      * The value format for hazard curves.
      *
@@ -246,6 +256,7 @@ public final class CalcConfig {
       this.sourceTypes = b.sourceTypes;
       this.vs30s = b.vs30s;
       this.gmmDampingRatio = b.gmmDampingRatio;
+      this.gmmSigmaScaling = b.gmmSigmaScaling;
       this.valueFormat = b.valueFormat;
 
       this.customImls = b.customImls;
@@ -287,6 +298,7 @@ public final class CalcConfig {
       Set<SourceType> sourceTypes;
       Set<Double> vs30s;
       Double gmmDampingRatio;
+      Double gmmSigmaScaling;
       ValueFormat valueFormat;
       Map<Imt, double[]> customImls;
       Map<Imt, XySequence> curveMap;
@@ -305,6 +317,11 @@ public final class CalcConfig {
             RezaeianDamping_2014.DAMPING_RATIO_RANGE,
             "gmmDampingRatio",
             gmmDampingRatio);
+        checkNotNull(gmmSigmaScaling);
+        checkInRange(
+            Range.closed(0.5, 1.0),
+            "gmmSigmaScaling",
+            gmmSigmaScaling);
         checkNotNull(valueFormat);
         checkNotNull(customImls);
         return new Hazard(this);
@@ -318,6 +335,7 @@ public final class CalcConfig {
         this.sourceTypes = that.sourceTypes;
         this.vs30s = that.vs30s;
         this.gmmDampingRatio = that.gmmDampingRatio;
+        this.gmmSigmaScaling = that.gmmSigmaScaling;
         this.valueFormat = that.valueFormat;
         this.customImls = that.customImls;
       }
@@ -344,6 +362,9 @@ public final class CalcConfig {
         if (that.gmmDampingRatio != null) {
           this.gmmDampingRatio = that.gmmDampingRatio;
         }
+        if (that.gmmSigmaScaling != null) {
+          this.gmmSigmaScaling = that.gmmSigmaScaling;
+        }
         if (that.valueFormat != null) {
           this.valueFormat = that.valueFormat;
         }
diff --git a/src/main/resources/calc/calc-config-defaults.json b/src/main/resources/calc/calc-config-defaults.json
index 7e3ace29cc17d1a6ac8c8412cef328fc62ab5e67..2de807379fd6a2b2c1b9d511d23ac232028539a3 100644
--- a/src/main/resources/calc/calc-config-defaults.json
+++ b/src/main/resources/calc/calc-config-defaults.json
@@ -13,7 +13,7 @@
     "sourceTypes": [],
     "vs30s": [],
     "gmmDampingRatio": 0.05,
-    "gmmSigmaReduction": 0.15,
+    "gmmSigmaScaling": 1.0,
     "valueFormat": "ANNUAL_RATE",
     "customImls": {}
   },
diff --git a/src/test/java/gov/usgs/earthquake/nshmp/calc/CalcConfigTests.java b/src/test/java/gov/usgs/earthquake/nshmp/calc/CalcConfigTests.java
index 9886fdeff0b6caa1ca52b1122ecf785618b632fc..91bafd901a32df139f352a673a5dd73cfb67eb7d 100644
--- a/src/test/java/gov/usgs/earthquake/nshmp/calc/CalcConfigTests.java
+++ b/src/test/java/gov/usgs/earthquake/nshmp/calc/CalcConfigTests.java
@@ -249,6 +249,7 @@ class CalcConfigTests {
     assertEquals(EnumSet.of(FAULT, ZONE, SLAB), def.sourceTypes);
     assertEquals(Set.of(260.0, 760.0), def.vs30s);
     assertEquals(0.03, def.gmmDampingRatio);
+    assertEquals(0.85, def.gmmSigmaScaling);
     assertEquals(ValueFormat.POISSON_PROBABILITY, def.valueFormat);
 
     assertArrayEquals(
@@ -263,6 +264,7 @@ class CalcConfigTests {
     assertEquals(EnumSet.noneOf(SourceType.class), def.tectonicSettings);
     assertEquals(Set.of(), def.vs30s);
     assertEquals(0.05, def.gmmDampingRatio);
+    assertEquals(1.0, def.gmmSigmaScaling);
     assertEquals(ValueFormat.ANNUAL_RATE, def.valueFormat);
   }
 
@@ -351,7 +353,7 @@ class CalcConfigTests {
 
   @Test
   void testOutputMember() {
-    List<Integer> defaultReturnPeroiods = List.of(475, 975, 2475);
+    List<Integer> defaultReturnPeroiods = List.of(475, 975, 2475, 10000);
 
     CalcConfig.Output def = DEFAULTS.output;
     assertEquals(Path.of("hazout"), def.directory);
diff --git a/src/test/resources/calc/calc-config-extends.json b/src/test/resources/calc/calc-config-extends.json
index f1f535f80947c972b714f97ef9831fc2006392a9..63a1758e405c11b2bd3c2997d1815c4c60bcea57 100644
--- a/src/test/resources/calc/calc-config-extends.json
+++ b/src/test/resources/calc/calc-config-extends.json
@@ -9,6 +9,7 @@
     "sourceTypes": [ "FAULT", "ZONE", "SLAB" ],
     "vs30s": [ 260, 760 ],
     "gmmDampingRatio": 0.03,
+    "gmmSigmaScaling": 0.85,
     "valueFormat": "POISSON_PROBABILITY",
     "customImls": {
       "PGA": [0.0025, 0.0075, 0.0169, 0.0380, 0.0854, 0.192, 0.432, 0.973, 2.19, 4.92]