Why is this value updating on each array inside my 2d array?

I have a 2d array:

let arr = [ [ 0, 0, 0, 0 ], [ 0, 0, 0, 0 ], [ 0, 0, 0, 0 ], [ 0, 0, 0, 0 ] ]

When I try to update the 1st sub array in the 2nd position with:

arr[0][1] = 4

The output is:

[ [ 0, 4, 0, 0 ], [ 0, 4, 0, 0 ], [ 0, 4, 0, 0 ], [ 0, 4, 0, 0 ] ]

Why are all of the sub arrays updating?

The full code is:

let arr = [ [ 0, 0, 0, 0 ], [ 0, 0, 0, 0 ], [ 0, 0, 0, 0 ], [ 0, 0, 0, 0 ] ]
arr[0][1] = 4
console.log(arr)