diff --git a/src/main/java/gov/usgs/earthquake/nshmp/gmm/Gmm.java b/src/main/java/gov/usgs/earthquake/nshmp/gmm/Gmm.java
index 5c8382f17c2222c1a9b8f42f227cf0edda4b787c..62b0ffdc3c035231af03a327bb45a5fc417994e5 100644
--- a/src/main/java/gov/usgs/earthquake/nshmp/gmm/Gmm.java
+++ b/src/main/java/gov/usgs/earthquake/nshmp/gmm/Gmm.java
@@ -470,6 +470,13 @@ public enum Gmm {
       ParkerEtAl_2020.COEFFS_INTERFACE,
       ParkerEtAl_2020.CONSTRAINTS_INTERFACE),
 
+  /** @see ParkerEtAl_2020 */
+  PSBAH_20_SEATTLE_INTERFACE_BASIN(
+      ParkerEtAl_2020.SeattleInterfaceBasin.class,
+      ParkerEtAl_2020.SeattleInterfaceBasin.NAME,
+      ParkerEtAl_2020.COEFFS_INTERFACE,
+      ParkerEtAl_2020.CONSTRAINTS_INTERFACE),
+
   /** @see ParkerEtAl_2020 */
   PSBAH_20_CASCADIA_SLAB_BASIN(
       ParkerEtAl_2020.CascadiaSlabBasin.class,
diff --git a/src/main/java/gov/usgs/earthquake/nshmp/gmm/ParkerEtAl_2020.java b/src/main/java/gov/usgs/earthquake/nshmp/gmm/ParkerEtAl_2020.java
index a3e5b737bbdfce250a124b7df5d6cb6390089615..b10e9fd98b02eeca543c6d83b2d26008cdba5bab 100644
--- a/src/main/java/gov/usgs/earthquake/nshmp/gmm/ParkerEtAl_2020.java
+++ b/src/main/java/gov/usgs/earthquake/nshmp/gmm/ParkerEtAl_2020.java
@@ -583,6 +583,24 @@ public abstract class ParkerEtAl_2020 implements GroundMotionModel {
     }
   }
 
+  static final class SeattleInterfaceBasin extends CascadiaInterface {
+    static final String NAME = CascadiaInterface.NAME + " (Seattle basin)";
+
+    SeattleInterfaceBasin(Imt imt) {
+      super(imt);
+    }
+
+    @Override
+    boolean basin() {
+      return true;
+    }
+
+    @Override
+    boolean seattle() {
+      return true;
+    }
+  }
+
   static final class CascadiaSlabBasin extends CascadiaSlab {
     static final String NAME = CascadiaSlab.NAME + " (basin)";