diff --git a/src/main/java/gov/usgs/earthquake/nshmp/model/InterfaceRuptureSet.java b/src/main/java/gov/usgs/earthquake/nshmp/model/InterfaceRuptureSet.java
index 8b965edb7d8904623e340f37fd5928f284b133ac..1351e5239af8dd69410de2efa14bc3f49130aacf 100644
--- a/src/main/java/gov/usgs/earthquake/nshmp/model/InterfaceRuptureSet.java
+++ b/src/main/java/gov/usgs/earthquake/nshmp/model/InterfaceRuptureSet.java
@@ -14,8 +14,6 @@ import java.util.Map;
 import java.util.function.Predicate;
 
 import gov.usgs.earthquake.nshmp.Earthquakes;
-import gov.usgs.earthquake.nshmp.fault.surface.ApproxGriddedSurface;
-import gov.usgs.earthquake.nshmp.fault.surface.GriddedSurface;
 import gov.usgs.earthquake.nshmp.geo.Location;
 import gov.usgs.earthquake.nshmp.geo.LocationList;
 import gov.usgs.earthquake.nshmp.geo.Locations;
@@ -40,8 +38,6 @@ public class InterfaceRuptureSet extends AbstractRuptureSet<InterfaceSource> {
   final LogicTree<Mfd> mfdTree;
   final Mfd mfdTotal;
 
-  final List<Integer> sectionIds;// reference: actually needed?
-  final GriddedSurface surface;
   private final List<InterfaceSource> source;
 
   InterfaceRuptureSet(Builder builder) {
@@ -52,8 +48,6 @@ public class InterfaceRuptureSet extends AbstractRuptureSet<InterfaceSource> {
     this.mfdTree = builder.mfdTree;
     this.mfdTotal = builder.mfdTotal;
 
-    this.sectionIds = builder.sectionIds;
-    this.surface = builder.surface;
     this.source = List.of(createSource());
   }
 
@@ -193,7 +187,6 @@ public class InterfaceRuptureSet extends AbstractRuptureSet<InterfaceSource> {
     /* created on build */
     private LogicTree<Mfd> mfdTree;
     private Mfd mfdTotal;
-    private GriddedSurface surface;
 
     private Builder() {
       super(SourceType.INTERFACE);
@@ -254,12 +247,6 @@ public class InterfaceRuptureSet extends AbstractRuptureSet<InterfaceSource> {
       mfdTotal = ModelTrees.reduceMfdTree(mfdTree);
 
       feature = createFeature();
-
-      SourceConfig.Interface config = data.sourceConfig().asInterface();
-      surface = new ApproxGriddedSurface(
-          feature.traces.get(0),
-          feature.traces.get(1),
-          config.surfaceSpacing);
     }
 
     private SourceFeature.Interface createFeature() {