Variations in fault maturity have intermittently been invoked to explain variations in some seismological observations for large earthquakes. However, the lack of a unified geological definition of fault maturity makes quantitative assessment of its importance difficult. We evaluate the degree of empirical correlation between field measurements indicative of fault zone maturity and remotely measured seismological source parameters of 34 large shallow strike-slip events. Metrics based on fault segmentation, such as number of primary rupture segments and surface rupture azimuth, correlate best with seismic source attributes and the correlations with cumulative fault slip are somewhat weaker. Average rupture velocity shows the strongest correlation with metrics of maturity, followed by relative aftershock productivity. Mature faults have relatively lower aftershock productivity and higher rupture velocity. A more complex relation is found with moment-scaled radiated energy. There appears to be distinct behavior of very immature events with no prior mapped fault and < 1 km cumulative slip, which radiate modest seismic energy, while moderately mature faults have events with higher moment-scaled radiated energy and very mature faults with increasing cumulative slip tend to have events with reducing moment-scaled radiated energy. We also explore qualitative and composite assessments of maturity and arrive at similar trends. This empirical approach establishes that there are relationships between remote seismological observations and fault system maturity that can help to understand variations in seismic hazard among different fault environments and to assess the relative maturity of blind fault systems for which direct observations of maturity are very limited.

The subduction zone along the northern Tonga Trench has the highest plate convergence rate in the world, but limited records of its seismic and tsunamigenic activities. In 2009, a tsunami generated by an MW 8.1 earthquake doublet caused severe impacts in the region including damage and loss of life on the south shores of Upolu and Savaii Islands, Samoa. Here we use numerical modeling aided by recorded data and eyewitness accounts to evaluate which of the published source models in the Tonga Trench region most suitably represents the 2009 event for use in hazard assessment around Samoa. We show that only a few of the published sources are suitable to reproduce large inundation observed in Samoa and none reproduces runup as high as observed in areas that were most severely impacted on the southeast Upolu coast. The distribution and intensity of inundation is dependent on local topographic and bathymetric features, configuration of coastal geomorphology, and trapping of short-period waves over the reef flats. For one of the sources, comparison of the relative contributions of the normal and thrust faulting components of the doublet to the southeast Upolu inundation indicates that the initial intraplate normal faulting dominated the east-northeastward tsunami propagation and inundation compared with the subsequent interplate thrust faulting. Overall, two key source models are discussed and identified for future refinement.