Comparison of Earthquake Strains Over 102 and 104 Year Timescales: Insights into the Variability In the Seismic Cycle In the Central Apennines, Italy

In order to study the existence of possible deficits or surpluses of geodetic and earthquake strain in the Lazio-Abruzzo region of the central Apennines compared to 15±3kyrs multi seismic cycle strain-rates, horizontal strain-rates are calculated in 5km×5km and 20km×20km grid squares using slip-vectors from striated faults and offsets of Late Pleistocene-Holocene landforms and sediments. Strain-rates calculated over 15±3kyrs within 5km×5km grid squares vary from zero up to 2.34±0.54×10^-7yr^-1 and resolve variations in strain orientations and magnitudes along the strike of individual faults. Strain-rates over a time period of 15±3kyrs from 5km×5km grid squares integrated over an area of 80km×160km show the horizontal strain-rate of the central Apennines is 1.22×10^-8yr^-1(error +0.1×10^-8yr^-1 -0.05×10^-8yr^-1) and -2.94×10^-10yr^-1(error +3.90×10^-10yr^-1 -4.55×10^-10yr^-1) parallel and perpendicular to the regional principal strain direction (42^o±1^o), associated with extension rates of ≤ 3.2mmyr^-1(error +0.8mmyr^-1 -0.4mmyr^-1) if calculated in 5km×80km boxes crossing the strike of the central Apennines. These strain-rates are comparable in direction to strain-rates calculated using GPS (over 126yrs, 11yrs and 5yrs) and seismic moment summation (over 700yrs), however the magnitude is about 2.4× less over a comparable area. 10²yr strain rates are higher than 10⁴yr strain-rates in some smaller areas (≈ 2000km², corresponding to polygons defined by GPS campaigns and seismic moment summations) with the opposite situation in other areas where seismic moment release rates in large (> Ms 6.0) magnitude historical earthquakes are as low as zero. This demonstrates the importance of comparing the exact same areas and that strain-rates vary spatially on the length scale of individual faults AND on a timescale between 10²yr and 10⁴yr in the central Apennines. We use these results to produce a fault specific earthquake recurrence interval map and discuss the regional deformation related to plate boundary and sub-crustal forces, temporal earthquake clustering and the natural variability of the seismic cycle.