In Dead Island 2, there exists a Legendary Revolver called the Big Shot, which is capable of delivering a devastating blow. But you can only acquire this weapon once you have completed the game, so it may not be of much help during your main game story.
Upon completing the main story, travel to Emma’s mansion in Bel-Air. Follow the Side Quest and talk to Luciana on the top floor. This will initiate the side quest.
Look for seismologists’ signage outside the drains
Go to the Bel-Air entrance to the Brentwood Sewers after deciding to assist Luciana in finding the missing scientists and seismometers. The driveway leading to the sewer access may be found outside Emma’s Mansion, close to the intersection of Access Rd 782 and Alpine Dr.
As you go closer to the door, you’ll notice a Journal next to a seismologist’s lifeless body leaning up against a white pickup vehicle.
Seismometer Placement Journal
This Journal lists the locations of all the seismometers hidden in the Brentwood Sewers:
Near the Bel-air accessway
Tunnel past Hydrostatics Management System
In Filtration Acess and Servicing
Inside the Main Septic Tank
To find the seismometers, enter the sewers.
To locate these seismometers, enter the Brentwood Sewer entry. As you pass by, take care! Putrfied Slobbers’ explosive pustules have adhered to the ceiling and the ground. One will explode and hurt you if you get too close to it. Step back swiftly with your Dodge after one of these pustules has been triggered to prevent splash damage. Continue by passing through and entering the Brentwood Sewers.
Find the first seismometer
You must first locate the keys to each of the seismometers buried in the Brentwood Sewers in order to open the chest. As you enter the sewers from the Bel-Air entrance, you may locate the first seismometer chest and key, Seismometer Alpha, just around the corner to the left.
Data from the second seismometer should be recovered.
Strive for the Venice Storm Tank tunnel. Numerous Apex Variant zombies, such as Firestorm Slobbers and Crushers, will be present along the way.
Seismometer Beta’s key is located in the northeastern part of the tunnel, immediately past the Automated Hydrostatics Monitoring chamber.
Just need to locate the seismometer itself now. The second seismometer is located across from the fuse room in the tunnel between Automated Hydrostatics and Filtration Access and Servicing, behind some bars in a wall of blood.
Get the data from the third seismometer
Until you reach Filtration Access and Servicing, continue travelling west. To access the control room office on the higher level, ascend the stairs on the right side. This is where you’ll discover the chest with the third seismometer and a journal, which is on a table against the back wall.
Take the catwalks over the blood and caustic liquid to the south side of the area, where you can then leap down and cross the blood to reach the lower level of the chamber. Another seismologist’s body is slumped against a wall as you walk in, along with a message on the floor.
Once the room is safe, search the piles of “meat slurry” for the key. You will find the key in the meat slurry pile right next to the seismologist’s corpse against the north wall.
Head back up to the control room office on the upper level of Filtration Access and Servicing, but beware… a Butcher has taken up residence within. With the Butcher taken care of, open up the third seismometer chest in the control room office.
Go to the main septic tank
Just the fourth seismometer remains now. The note’s claim that it was left in the Main Septic Tank—also known as the “Heart of Darkness”—is ominous news. To retrieve this final device, you must re-enter the pit of blood and undead.
There are several challenging adversaries waiting for you as soon as you enter the Main Septic Tank, including Caustic-X Walkers, Crushers, Bursters, and Slobbers.
The Maintenance Worker, though, might be the most worrying. You must defeat this Butcher Apex Variant before reaching the last seismometer because he hides in the Main Septic Tank’s depths. The Maintenance Toolbox Key will be dropped by the downed Maintenance Worker zombie.
Kill the Seismologist
The Seismologist zombie can be found in the back of the Main Septic Tank, close to the stairs that go up to the scaffolding. This Electrified Runner has electricity running through its zombie’s veins, and at predetermined times, it will erupt into an electric cloud. Ensure that when it goes off, you are out of the way.
The last key—Seismometer Key Delta—is dropped once the seismologist has passed away.
To the left of where you discovered the Seismologist, amid a pile of hamburger slurry, is where you can find the fourth seismometer chest. The final bit of information is inside the chest, so open it.
You will trigger a powerful earthquake as soon as you do. There will be zombies everywhere, including Mutators and Voltaic Screamers. There isn’t much room for escape this time, quite literally. Before leaving the Main Septic Tank, you must eliminate this wave of zombies.
Finally, you may say goodbye permanently to the Brentwood Sewers. To go back to Bel-Air, use the nearest exit or the Fast Travel map.
Speak with Luciana
Return to Emma’s Mansion in Bel-Air to meet Luciana. She handles the news of her fellow scientists’ deaths (and resurrections) quite well, but she is even more appreciative that the seismometer data have been obtained. She rewards you handsomely with a legendary gun in exchange.