How deep can we go into earth's interior?

So far, the "Kola Superdeep Borehole" is the deepest artificial point on Earth.
Drilling began in the Pechengsky District of the old Soviet Union in May 1970,
and after 19 years, it reached 12,262 meters. (That's 40,230 feet, or about 7.6
miles.)  Although that was 25 years ago, nothing has been drilled deeper, and
it's still the record.

7.6 miles is something like 0.19 percent of the distance to the Earth's center.

There can be more freedom for them

Earthquake waves that vibrate from side to side and up and down only through solids are known as "seismic waves."hope my answer has you : )