diff --git a/tests/unit-tests/displacement_tests/Newmark/serial/test3/database.bin b/tests/unit-tests/displacement_tests/Newmark/serial/test3/database.bin
index 8bb86ad7..7686edce 100644
Binary files a/tests/unit-tests/displacement_tests/Newmark/serial/test3/database.bin and b/tests/unit-tests/displacement_tests/Newmark/serial/test3/database.bin differ
diff --git a/tests/unit-tests/displacement_tests/Newmark/serial/test3/displacement.bin b/tests/unit-tests/displacement_tests/Newmark/serial/test3/displacement.bin
index c3cf7067..5b67dbbb 100644
Binary files a/tests/unit-tests/displacement_tests/Newmark/serial/test3/displacement.bin and b/tests/unit-tests/displacement_tests/Newmark/serial/test3/displacement.bin differ
diff --git a/tests/unit-tests/displacement_tests/Newmark/serial/test3/potential_acoustic.bin b/tests/unit-tests/displacement_tests/Newmark/serial/test3/potential_acoustic.bin
index 573ba2a7..1b83e332 100644
Binary files a/tests/unit-tests/displacement_tests/Newmark/serial/test3/potential_acoustic.bin and b/tests/unit-tests/displacement_tests/Newmark/serial/test3/potential_acoustic.bin differ
diff --git a/tests/unit-tests/displacement_tests/Newmark/serial/test3/sources.yaml b/tests/unit-tests/displacement_tests/Newmark/serial/test3/sources.yaml
index 1c9cb90c..6e5485ab 100644
--- a/tests/unit-tests/displacement_tests/Newmark/serial/test3/sources.yaml
+++ b/tests/unit-tests/displacement_tests/Newmark/serial/test3/sources.yaml
@@ -2,7 +2,7 @@ number-of-sources: 1
 sources:
   - force:
       x : 1575.0
-      z : 2405.0
+      z : 2420.0
       source_surf: false
       angle : 0.0
       vx : 0.0
diff --git a/tests/unit-tests/displacement_tests/Newmark/serial/test3/specfem_config.yaml b/tests/unit-tests/displacement_tests/Newmark/serial/test3/specfem_config.yaml
index 0043c06f..5adebc18 100644
--- a/tests/unit-tests/displacement_tests/Newmark/serial/test3/specfem_config.yaml
+++ b/tests/unit-tests/displacement_tests/Newmark/serial/test3/specfem_config.yaml
@@ -1,12 +1,15 @@
+## Coupling interfaces have code flow that is dependent on orientation of the interface.
+## This test is to check the code flow for horizontal acoustic-elastic interface with acoustic domain on top.
+
 parameters:
 
   header:
     ## Header information is used for logging. It is good practice to give your simulations explicit names
-    title: Heterogeneous acoustic-elastic medium with 1 acoustic-elastic interface # name for your simulation
+    title: Heterogeneous acoustic-elastic medium with 1 acoustic-elastic interface (orientation horizontal)  # name for your simulation
     # A detailed description for your simulation
     description: |
       Material systems : Elastic domain (1), Acoustic domain (1)
-      Interfaces : Acoustic-elastic interface (1)
+      Interfaces : Acoustic-elastic interface (1) (orientation horizontal with acoustic domain on top)
       Sources : Force source (1)
       Boundary conditions : Neumann BCs on all edges
 
@@ -24,8 +27,8 @@ parameters:
         type-of-simulation: forward
         time-scheme:
           type: Newmark
-          dt: 0.85e-3
-          nstep: 500
+          dt: 1.90e-3
+          nstep: 100
 
   receivers:
     stations-file: "../DATA/STATIONS"
diff --git a/tests/unit-tests/displacement_tests/Newmark/serial/test4/database.bin b/tests/unit-tests/displacement_tests/Newmark/serial/test4/database.bin
new file mode 100644
index 00000000..e73fcc60
Binary files /dev/null and b/tests/unit-tests/displacement_tests/Newmark/serial/test4/database.bin differ
diff --git a/tests/unit-tests/displacement_tests/Newmark/serial/test4/displacement.bin b/tests/unit-tests/displacement_tests/Newmark/serial/test4/displacement.bin
new file mode 100644
index 00000000..8a41956d
Binary files /dev/null and b/tests/unit-tests/displacement_tests/Newmark/serial/test4/displacement.bin differ
diff --git a/tests/unit-tests/displacement_tests/Newmark/serial/test4/potential_acoustic.bin b/tests/unit-tests/displacement_tests/Newmark/serial/test4/potential_acoustic.bin
new file mode 100644
index 00000000..1dade099
Binary files /dev/null and b/tests/unit-tests/displacement_tests/Newmark/serial/test4/potential_acoustic.bin differ
diff --git a/tests/unit-tests/displacement_tests/Newmark/serial/test4/sources.yaml b/tests/unit-tests/displacement_tests/Newmark/serial/test4/sources.yaml
new file mode 100644
index 00000000..6e5485ab
--- /dev/null
+++ b/tests/unit-tests/displacement_tests/Newmark/serial/test4/sources.yaml
@@ -0,0 +1,13 @@
+number-of-sources: 1
+sources:
+  - force:
+      x : 1575.0
+      z : 2420.0
+      source_surf: false
+      angle : 0.0
+      vx : 0.0
+      vz : 0.0
+      Ricker:
+        factor: 1e9
+        tshift: 0.0
+        f0: 10.0
diff --git a/tests/unit-tests/displacement_tests/Newmark/serial/test4/specfem_config.yaml b/tests/unit-tests/displacement_tests/Newmark/serial/test4/specfem_config.yaml
new file mode 100644
index 00000000..709c5432
--- /dev/null
+++ b/tests/unit-tests/displacement_tests/Newmark/serial/test4/specfem_config.yaml
@@ -0,0 +1,53 @@
+## Coupling interfaces have code flow that is dependent on orientation of the interface.
+## This test is to check the code flow for horizontal acoustic-elastic interface with acoustic domain on bottom.
+
+parameters:
+
+  header:
+    ## Header information is used for logging. It is good practice to give your simulations explicit names
+    title: Heterogeneous acoustic-elastic medium with 1 acoustic-elastic interface (orientation horizontal)  # name for your simulation
+    # A detailed description for your simulation
+    description: |
+      Material systems : Elastic domain (1), Acoustic domain (1)
+      Interfaces : Acoustic-elastic interface (1) (orientation horizontal with acoustic domain on bottom)
+      Sources : Force source (1)
+      Boundary conditions : Neumann BCs on all edges
+
+  simulation-setup:
+    ## quadrature setup
+    quadrature:
+      alpha: 0.0
+      beta: 0.0
+      ngllx: 5
+      ngllz: 5
+
+    ## Solver setup
+    solver:
+      time-marching:
+        type-of-simulation: forward
+        time-scheme:
+          type: Newmark
+          dt: 1.90e-3
+          nstep: 100
+
+  receivers:
+    stations-file: "../DATA/STATIONS"
+    angle: 0.0
+    seismogram-type:
+      - displacement
+      - velocity
+    nstep_between_samples: 1
+
+  ## Runtime setup
+  run-setup:
+    number-of-processors: 1
+    number-of-runs: 1
+
+  ## databases
+  databases:
+    mesh-database: "../../../tests/unit-tests/displacement_tests/Newmark/serial/test4/database.bin"
+    source-file: "../../../tests/unit-tests/displacement_tests/Newmark/serial/test4/sources.yaml"
+
+  seismogram:
+    seismogram-format: ascii
+    output-folder: "."
diff --git a/tests/unit-tests/displacement_tests/Newmark/test_config.yaml b/tests/unit-tests/displacement_tests/Newmark/test_config.yaml
index 1d1e6a9b..b5f5a30f 100644
--- a/tests/unit-tests/displacement_tests/Newmark/test_config.yaml
+++ b/tests/unit-tests/displacement_tests/Newmark/test_config.yaml
@@ -17,12 +17,22 @@ Tests:
       specfem_config: "../../../tests/unit-tests/displacement_tests/Newmark/serial/test2/specfem_config.yaml"
       acoustic_domain_field: "../../../tests/unit-tests/displacement_tests/Newmark/serial/test2/potential_acoustic.bin"
 
-  - name : "SerialTest3 : Acoustic-Elastic coupled domain"
+  - name : "SerialTest3 : Acoustic-Elastic coupled domain (Test 1/2)"
     description: >
-      Testing newmark time-marching solver on a coupled acoustic-elastic domain with 1 elastic-acoustic interface. Test is run on a single MPI process.
+      Testing newmark time-marching solver on a coupled acoustic-elastic domain with 1 elastic-acoustic interface. The orientation of the interface is horizontal with acoustic domain on top. Test is run on a single MPI process.
     config:
       nproc : 1
     databases:
       specfem_config: "../../../tests/unit-tests/displacement_tests/Newmark/serial/test3/specfem_config.yaml"
       acoustic_domain_field: "../../../tests/unit-tests/displacement_tests/Newmark/serial/test3/potential_acoustic.bin"
       elastic_domain_field: "../../../tests/unit-tests/displacement_tests/Newmark/serial/test3/displacement.bin"
+
+  - name : "SerialTest4 : Acoustic-Elastic coupled domain (Test 2/2)"
+    description: >
+      Testing newmark time-marching solver on a coupled acoustic-elastic domain with 1 elastic-acoustic interface. The orientation of the interface is horizontal with acoustic domain on bottom. Test is run on a single MPI process.
+    config:
+      nproc : 1
+    databases:
+      specfem_config: "../../../tests/unit-tests/displacement_tests/Newmark/serial/test4/specfem_config.yaml"
+      acoustic_domain_field: "../../../tests/unit-tests/displacement_tests/Newmark/serial/test4/potential_acoustic.bin"
+      elastic_domain_field: "../../../tests/unit-tests/displacement_tests/Newmark/serial/test4/displacement.bin"