Article,
Seismic sources and attenuation properties at the Campi Flegrei volcanic area
Pure and Applied Geophysics, 125 (6): 883--917 (Nov 1, 1987)
DOI: 10.1007/BF00879360
Abstract
Microearthquake digital data collected at Campi Flegrei during the
recent (1982-1985) ground uplift episode have been analyzed in order
to infer source and medium seismic properties. The main results obtained
from these analyses are: 1. Hypocenter distribution and the size
of the seismic zone do not change with time and do not depend on
the ground uplift rate. Events occurred clustered in time with no
simple causal relations between the cluster occurrences and their
energy. 2. Anelastic attenuation does not depend strongly on frequency,
showing a constant pattern at high frequencies. The observed values
of low and high frequency attenuation, due to the short source receiver
distances,do not seriously affect the spectral content of signals
radiated by the sources. 3. A constant Brune stress drop pattern
(4-5 bars) as a function of seismic moment is observed. This indicates
that the manner of fracturing is almost independent on magnitude
of earthquakes (hypothesis of self-similarity (Aki, 1967)). Seismic
processes in a prefractured medium can explain the observed small
stress drop values. 4. Focal mechanisms from moment tensor estimates
show that radiation patterns are mostly well interpreted in terms
of double couple source models. 5. The scaling of peak ground motion
parameters (Amax and Vmax vs seismic moment) can be explained by
an omega^2 source model (constant stress drop) multiplied by an exponential
function with a small decay parameter, which takes into account the
measured attenuation. These results support the hypothesis of earthquakes
generated by simple shear fractures along prefractured structures
as a response to changes in the stress field due to the ground deformation.
