diff --git a/common/main/multi.h b/common/main/multi.h
index dbe5afee1..6f7b9cbb6 100644
--- a/common/main/multi.h
+++ b/common/main/multi.h
@@ -452,7 +452,7 @@ void multi_send_wall_status_specific (playernum_t pnum,int wallnum,ubyte type,ub
 void multi_send_light_specific (playernum_t pnum,segnum_t segnum,ubyte val);
 void multi_send_capture_bonus (playernum_t pnum);
 int multi_all_players_alive();
-void multi_send_seismic (fix64,fix64);
+void multi_send_seismic(fix);
 void multi_send_drop_blobs(playernum_t);
 void multi_send_sound_function (char,char);
 void DropFlag();
diff --git a/common/main/multiinternal.h b/common/main/multiinternal.h
index dc2a40bc0..04ed1e3fc 100644
--- a/common/main/multiinternal.h
+++ b/common/main/multiinternal.h
@@ -84,7 +84,7 @@
 	VALUE(MULTI_GUIDED               , 3+sizeof(shortpos))	\
 	VALUE(MULTI_STOLEN_ITEMS         , 11)	\
 	VALUE(MULTI_WALL_STATUS          , 6)	/* send to new players */	\
-	VALUE(MULTI_SEISMIC              , 9)	\
+	VALUE(MULTI_SEISMIC              , 5)	\
 	VALUE(MULTI_LIGHT                , 18)	\
 	VALUE(MULTI_START_TRIGGER        , 2)	\
 	VALUE(MULTI_FLAGS                , 6)	\
diff --git a/common/main/weapon.h b/common/main/weapon.h
index 984c44647..34baeac3b 100644
--- a/common/main/weapon.h
+++ b/common/main/weapon.h
@@ -358,7 +358,7 @@ static inline int weapon_index_is_player_bomb(unsigned id)
 	return id == PROXIMITY_INDEX;
 }
 #elif defined(DXX_BUILD_DESCENT_II)
-extern fix64	Seismic_disturbance_start_time, Seismic_disturbance_end_time;
+extern fix64 Seismic_disturbance_end_time;
 int which_bomb(void);
 
 static inline int weapon_index_uses_vulcan_ammo(unsigned id)
diff --git a/similar/main/multi.cpp b/similar/main/multi.cpp
index 8c1a2dddf..96bf063c9 100644
--- a/similar/main/multi.cpp
+++ b/similar/main/multi.cpp
@@ -3837,19 +3837,16 @@ void multi_check_for_killgoal_winner ()
 
 #if defined(DXX_BUILD_DESCENT_II)
 // Sync our seismic time with other players
-void multi_send_seismic (fix64 t1,fix64 t2)
+void multi_send_seismic(fix duration)
 {
 	int count=1;
-
-	PUT_INTEL_INT(multibuf+count, t1); count+=(sizeof(fix));
-	PUT_INTEL_INT(multibuf+count, t2); count+=(sizeof(fix));
+	PUT_INTEL_INT(&multibuf[count], duration); count += sizeof(duration);
 	multi_send_data<MULTI_SEISMIC>(multibuf, count, 2);
 }
 
 static void multi_do_seismic (const ubyte *buf)
 {
-	fix duration = GET_INTEL_INT(buf + 5);
-	Seismic_disturbance_start_time = GameTime64;
+	const fix duration = GET_INTEL_INT(&buf[1]);
 	Seismic_disturbance_end_time = GameTime64 + duration;
 	digi_play_sample (SOUND_SEISMIC_DISTURBANCE_START, F1_0);
 }
diff --git a/similar/main/weapon.cpp b/similar/main/weapon.cpp
index 0731e97dd..ef9666a64 100644
--- a/similar/main/weapon.cpp
+++ b/similar/main/weapon.cpp
@@ -945,48 +945,41 @@ void rock_the_mine_frame(void)
 	//	Hook in the rumble sound effect here.
 }
 
-#define	SEISMIC_DISTURBANCE_DURATION	(F1_0*5)
-fix64	Seismic_disturbance_start_time = 0, Seismic_disturbance_end_time;
-
-int Seismic_level=0;
-
+fix64 Seismic_disturbance_end_time;
 void init_seismic_disturbances(void)
 {
-	Seismic_disturbance_start_time = 0;
 	Seismic_disturbance_end_time = 0;
 }
 
 //	Return true if time to start a seismic disturbance.
-static int start_seismic_disturbance(void)
+static bool seismic_disturbance_active()
 {
-	int	rval;
-
 	if (Level_shake_duration < 1)
-		return 0;
+		return false;
 
+	if (Seismic_disturbance_end_time && Seismic_disturbance_end_time < GameTime64)
+		return true;
+
+	const fix level_shake_duration = Level_shake_duration;
+	bool rval;
 	rval =  (2 * fixmul(d_rand(), Level_shake_frequency)) < FrameTime;
 
 	if (rval) {
-		Seismic_disturbance_start_time = GameTime64;
-		Seismic_disturbance_end_time = GameTime64 + Level_shake_duration;
+		Seismic_disturbance_end_time = GameTime64 + level_shake_duration;
 		start_seismic_sound();
 		if (Game_mode & GM_MULTI)
-			multi_send_seismic (Seismic_disturbance_start_time,Seismic_disturbance_end_time);
+			multi_send_seismic(level_shake_duration);
 	}
-
 	return rval;
 }
 
 static void seismic_disturbance_frame(void)
 {
 	if (Level_shake_frequency) {
-		if (((Seismic_disturbance_start_time < GameTime64) && (Seismic_disturbance_end_time > GameTime64)) || start_seismic_disturbance()) {
-			fix	delta_time;
+		if (seismic_disturbance_active()) {
 			int	fc, rx, rz;
-
-			delta_time = GameTime64 - Seismic_disturbance_start_time;
-
-			fc = abs(delta_time - (Seismic_disturbance_end_time - Seismic_disturbance_start_time)/2);
+			fix delta_time = static_cast<fix>(GameTime64 - Seismic_disturbance_end_time);
+			fc = abs(delta_time - Level_shake_duration / 2);
 			fc /= F1_0/16;
 			if (fc > 16)
 				fc = 16;