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The CE 1303 Hongdong earthquake, with ~270,000 deaths, has been suggested as the first magnitude 8 earthquake recorded in North China. We use 31 AMS‐14C ages to date earthquakes recorded in the Huoshan Piedmont Fault, which is interpreted to be the causative fault for the event. We interpret fault traces and map the Hongdong earthquake surface rupture in detail. Four events are identified with timings constrained at 1,060–590 year BP (corresponding to the Common Era 1303 event), 3,310–3,210 year BP, 5,460–5,380 year BP, and 26,380 year BP, respectively. The later three events have a recurrence interval of ~2,000–3,000 years. We find that the Hongdong earthquake had a rupture length of ~98 km, a maximum throw of 5.0 m and a best estimate for magnitude in the range Mw 7.2–7.6. We suggest that previous magnitude estimates are overestimates. Normal fault earthquakes have smaller upper limits to their magnitudes than thrusts, because their relatively steep dips produce intersections at the base of the seismogenic layer at smaller downdip widths than gently dipping thrust faults. The Hongdong event was not an exception to this pattern. The historic released seismic moment may be closer to the accumulated moment than previously calculated.

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Assessing the seismic hazard of a fault is usually based on its record of strong earthquakes. Earthquake records with long periods of quiescence for active faults can lead to underestimates of seismic hazards, such as for the Longmenshan fault zone which produced the unanticipated 2008 Mw 7.9 Wenchuan earthquake. The Daliangshan fault zone has a low slip rate and has not produced any strong earthquakes in history. As a result, little is known about its paleoearthquake history, including the behavior of any strong earthquakes it might produce and the seismic hazards posed by the Daliangshan fault zone. To solve this problem, we excavated four trenches across the Jiaojihe and Butuo faults along the southern segment of the Daliangshan fault zone. The paleoseismic investigations revealed six paleoearthquakes on the Jiaojihe fault in ~20,000 years and determined another seven rupturing events on the Butuo fault in ~42,000 years. The strong earthquake history of the Jiaojihe fault has evidence of temporal clustering, while the Butuo fault exhibits a relatively periodic recurrence pattern with intervals of 1,710–2,460 years. Based on its surface rupture length and the magnitude of observed displacement, the southern segment of the Daliangshan fault zone is capable of producing M > 6.5 earthquakes. Furthermore, based on their respective slip rates and the elapsed times since the most recent events along the Jiaojihe and Butuo faults, they have accumulated seismic energy equivalent to M ~ 7.6, suggesting they pose a significant seismic hazard to the southeastern Tibetan Plateau.

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