Correlating earthquake static stress drop values with fault complexity
in the 2016 Amatrice-Norcia earthquake sequence, Central Italy
Abstract
The 2016 Amatrice-Norcia seismic sequence in central Italy activated a
system of normal faults in the central Apennines and ruptured the
surface along the Monte Vettore normal fault. Due to the complex rupture
behavior, including antithetic faults and the proposed reactivation of
an old thrust front, the Amatrice-Norcia seismic sequence offers a
unique opportunity to study the relationship between fault complexity,
surface ruptures, and earthquake source properties. Here, we focus on
the first two months of the Amatrice-Norcia seismic sequence, including
the 30 October 2016 Mw 6.5 mainshock near Norcia and more than 25000
aftershocks. Using continuous waveform data from 94 seismic stations
with epicentral distances of up to ~100 km, we estimate
source parameters of all cataloged earthquakes that exceed specific
quality control criteria in a time period ranging from 24 October – 29
November 2016. Displacement spectral corner frequency and seismic moment
values are fit using individual earthquake spectra, and corner frequency
estimates are refined using spectral ratios. Constrained spectral
parameters then provide input for static stress drop estimates based on
a circular crack model. Preliminary results suggest the majority of
earthquakes have static stress drop values between 1 and 10 MPa and
self-similar scaling. Due to the high quality and quantity of available
data, including precise earthquake locations, manually reviewed phase
arrivals, and detailed mapping of surface ruptures, the Amatrice-Norcia
earthquake sequence represents an opportunity to link earthquake source
parameters to geological structures and surface rupture complexity.
Preliminary results show correlations between high stress drop values
and areas with increasing fault complexity, such as fault intersections
at depth (inferred from precise earthquake hypocenters) or the mapped
tip of the Monte Vettore normal fault, relative to other fault patches
with fewer intersections or mapped surface trace terminations. Future
work will examine whether the correlation of stress drop and fault
complexity holds using refined stress drop estimates obtained using
spectral ratio approaches.