Tectonic History and Seismicity in the Lunar North Polar Region: New Insights From the Geometry, Kinematics, Resurfacing Ages, and Seismic Hazard Potential of Lobate Scarps

Abstract

Lunar surface manifested a variety of tectonic structures in which lobate scarps (shallow thrust faults) are wide-spread globally. Despite many previous studies, the formation characteristics of lobate scarps in the lunar polar regions are poorly known. Earlier, we studied the geometry, kinematics, formation ages and seismic hazard potential of scarps in the lunar south polar region. In this study, we focused on the lunar north polar region, where we newly detected >280 individual lobate scarp segments and characterized their morphologic properties and formation ages. Orientations and movement directions of these scarps show spatial and latitudinal variations. Many scarps show pole-ward movements. We dated 105 scarp segments using the conventional crater counting method. Counting of fresh craters on these scarps yielded a majority age range of 4.8–75 Ma, while counting of all craters yielded 11–470 Ma range. These are interpreted to be the resurfacing ages of scarps due to seismic resetting, which occurred mostly in the last 100 million years. The fault ages indicate contemporaneous tectonic activity in different parts of the polar region. The lengths of majority scarp segments indicate their shallower fault depths (∼1 km) that are capable of producing small to medium size shallow moonquakes. The epicentral distances of many shallow moonquakes detected from the Apollo data coincide with the north polar lobate scarps. Considering M_W 1–4 shallow moonquakes along the lobate scarps, we provided a deterministic seismic hazard scenario. We conclude that lobate scarps in the lunar polar regions have a contrasting spatial distribution pattern and kinematic properties.