It is a long crack in the earth's crust where two tectonic plates move past each other.
The fault has been active since the Middle Miocene period, about 15 million years ago.
However, since the Plio-Pleistocene period, about 5 million years ago, the fault has changed into a left strike-slip fault, meaning that the plates are sliding horizontally past each other in opposite directions.
[3][4] This fault also possibly has caused a magnitude Mw 7.0 earthquake in 1833.
[6] Soft ground conditions around the northern part of the fault such as in Bekasi and Jakarta can cause amplification of earthquake shocks.