We performed nonadiabatic quantum wave packet dynamics calculations to simulate the photodetachment spectrum of the GeH2- (B-2(1)) anion. We developed the (4 x 4) diabatic potential energy surfaces to describe the intersystem crossing transitions between the neutral (1)A(1) and B-3(1) states induced by spin-orbit interactions based on ab initio calculations. The spin orbit coupling matrix elements were calculated using the Breit-Pauli Hamiltonian with the spin-free states obtained from the multireference configuration interaction method. The calculated photodetachment spectrum showed many intense peaks that could be assigned to the vibrational states mostly associated with the pure singlet or triplet spin states. However, we also found weak satellite peaks that could be assigned to vibrational states consisting of the highly excited vibrational state on the singlet surface and the low-lying vibrational state on the triplet surface.