TM26 Earthquake

TM26 Earthquake is located deep inside Seafloor Cavern, which is a cave underneath Route 128. You will need Pokémon that can use HM03 Surf and HM07 Dive outside of battle to access the exact location.

To reach the deepest part of the cave, you’ll also need to solve a few puzzles requiring you to have a Pokémon that knows HM04 Strength.

Prerequisites

You first gain access to the Seafloor Cavern while hunting down Team Aqua or Team Magma as part of the main story.

But there are some prerequisites you’ll need before you can get TM26, so make sure you do the following first:

• Obtain up to the seventh Gym Badge from Liza and Tate, Mossdeep City’s Gym Leaders. The Mind Badge allows you to use HM07 Dive outside of battle.
• Bring a Pokémon that knows HM03 Surf
• Bring a Pokémon that knows HM04 Strength
• Bring a Pokémon that knows HM07 Dive

Location

Once you’re all set, fly to Route 128:

Step 1: Use HM03 Surf here from the Route 128 sign and start heading west.

Step 2: Keep going west until you find a small sand bar. Then use HM07 Dive to go underwater just south of the sand bar (pictured below).

Step 3: Enter the cave underwater.

Step 4: Return to the surface.

Step 5: Surf north until you reach the entrance of the cave.

Step 6: Go through the door on the north to enter the next room.

Step 7: Head north and turn right near the breakable rock. You can pass directly next to this rock, so you aren’t required to break it.

Step 8: Head past the rock and start going north once again.

Step 9: Instead of going up the stairs here, turn left and go through the north cavern doorway (pictured below).

Step 10: In this new room you’ll want to follow the path heading west.

Step 11: Use HM04 Strength to push the boulder on the left side into the hole. Then keep moving north.

Step 12: Go through the next door on the northwest side of the room.

Step 13: This will take you to a body of water. Use HM03 Surf on the body of water.

Step 14: To get to the northeast side of the room, Surf on the water current going north.

Step 15: After that, the current will drop you onto a small square of water. From here, Surf on the water current to the left (this current will also take you north).

Step 16: Eventually you’ll see a section of land in the top-right corner of the screen. Go through the door in this northeastern side of the room.

Step 17: In the new room you’ll want to move up the set of stairs, then push the boulder to the right to walk around it.

Step 18: Then continue heading north.

Step 19: Keep going north until you see a new cavern door. Go through the door to enter the next room with the last puzzle in Seafloor Cavern.

Step 20: This room will contain a number of boulders. The first two you can access are on the left & right side.

Use HM04 Strength to push both boulders into the nearby holes.

Step 21: In the second row, push the boulder located on the right over to the left (pictured below).

Step 22: Walk to the third boulder located in the next row (up & to the right).

Step 23: Push this top-right boulder into the hole directly above it. Then you can continue forward.

Step 24: If you did it correctly, you should have access to the door on the northern side of this room. If not, leave to the south & then re-enter the room to reset the boulders’ positions.

Step 25: In the new room, follow the path heading east.

Step 26: Then follow the path heading south.

Step 27: Eventually this area will wrap over to the left, so you’ll want to follow the path on the left, but don’t go down the stairs.

Step 28: TM26 Earthquake should be on the ground in the furthest left corner, just before the staircase.