While landslides have been extremely researched, there is a notable gap in the literature regarding the combined impact of precipitation-induced and earthquake-induced landslide events on a large scale. This study presents an approach to evaluate pre-conditioned compound hazards, examining the individual and combined effects of seismic and precipitation-induced landslides. Utilizing a diverse dataset comprising precipitation, seismic, geological, and geotechnical data, the analysis includes assessments of seismic sliding displacements and precipitation-induced slope stability over a wide geographic area (Iran with ~ 1.7 million km2). We conducted discrete and joint hazard analyses to gain insights into combined seismic and precipitation-induced landslide hazards. A total of over 39,000 analyses were conducted to portray the proposed framework. The analysis indicated a higher likelihood of slope failure during earthquakes compared to precipitation-induced events. However, the combined impacts of both hazards result in significantly elevated hazard levels according to our assessments. Specifically, the joint analysis revealed that the sequence order of events can influence hazard levels. When an earthquake follows heavy precipitation, the landslide hazard level significantly increases compared to when precipitation follows an earthquake. These findings suggest that a discrete hazard analysis may underestimate hazards compared to a joint hazard analysis, especially when events occur sequentially. Comparisons between predicted and observed hazards for historical cases support the effectiveness of our proposed approach in predicting hazard levels. Overall, our proposed compound landslide hazard analysis provides a valuable tool for risk assessment and preparedness, aiding in mitigating the impact of pre-conditioned landslides.
