Seismic hazard assessments for the Ordos Block and its periphery in China

• The seismic hazard was estimated from more than 500 years of intensity observations.
• The intensity observations include site-effect and directly related to damage.
• Current design PGA or intensity for the Ordos Block may not be adequate.

Seismic hazards in the Ordos Block and its periphery were estimated based on 500 years of intensity observations. Firstly, historical intensity observations were collected, the completeness of the earthquake catalog was tested, and aftershocks were deleted. Secondly, the intensity data were digitized and placed in a geographic information system (GIS). Finally, the digitized intensity data were analyzed to determine the frequency–intensity relationship (i.e., seismic hazard curve) for each cell. The seismic hazards were quantified by the intensity and return period in a site or an area. Assuming a Poisson distribution for the earthquake occurrence in time, a probability of I≥VII, VIII, or IX in 50 years was quantified. We also estimated the corresponding intensities with 10% probability of exceedance in 50 years. The results show that the periphery of Ordos Block faces significant seismic hazards. Our study also suggests that the current designed peak ground acceleration or intensity for Ordos Block may not be adequate.