•The Quaternary Tan-Lu fault zone in the Bohai Bay consists of two main faults dipping steeply to the west.•The Tan-Lu fault zone was dominated by reverse dextral slip during the Holocene.•The Tan-Lu fault zone in the southern and central sections of the Bohai Bay was last active during the Holocene.•The ENE–WSW compression led to the Holocene faulting associated with many recent earthquakes in the Bohai Bay. The middle segment of the NNE–SSW-striking Tan-Lu Fault Zone (TLFZ) crosses the Bohai Bay in East China. This fault zone is a large seismically active belt that was responsible for the 1969 M (magnitude) 7.4 Bohai earthquake. However, the geometry, kinematics, and detailed characteristics of the most recent Quaternary seismic activity along the TLFZ in the Bohai Bay area are debated, primarily as the fault crops out below sea level in this area. Here, we present the results of a series of seismic profiles that enable the identification of Quaternary activity along the TLFZ within the Bohai Bay area. These data indicate that the Quaternary TLFZ crops out over a wide area of the Bohai Bay and is dominated by two main faults, both of which dip steeply to the west. Each of these two main faults consists of several left-stepping en-echelon faults. Quaternary activity along the TLFZ was generally focused along pre-existing Paleogene–Neogene faults. The seismic profiles, combined with the distribution of earthquakes in this area, demonstrate that the TLFZ in the southern and central areas of the Bohai Bay was last active during the Holocene, whereas the last movements along the faults in the northern Bohai Bay area range from late Pleistocene in the south to early–middle Pleistocene and the end of the Neogene in the north. The seismic profiles show both normal and reverse offset of the base of the Quaternary sediments by the Tan-Lu faults, although the normal offset predominates. Anticlines developed in Quaternary sediments occur close to the Quaternary Tan-Lu faults, and the TLFZ is also associated with an angular unconformity between Holocene and Pleistocene sediments. It is likely that the TLFZ was dominated by reverse dextral slip during the Holocene, whereas all of the Quaternary faulting before this involved alternating reverse and normal dextral slip. Oblique extension is most likely responsible for the normal dextral slip along the TLFZ, whereas focal mechanisms, GPS (global positioning system) data, and in situ stress measurements all suggest that ENE–WSW compression led to the reverse dextral faulting associated with numerous recent earthquakes in the Bohai Bay area.