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| Titel |
A regional fault-specific earthquake recurrence interval map for the Italian Apennines derived from post 15 ka strain-rate fields: implications for surpluses and deficits of seismic strain. |
| VerfasserIn |
Gerald Roberts, Joanna Faure Walker, Peter Sammonds, Patience Cowie, Alessandro Michetti |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036179
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| Zusammenfassung |
| A key unknown is how far a fault can stray from its long-term slip rate, both at a timescale
equivalent to the interseismic period (102-103 years), and over timescales equivalent to
several seismic cycles (103-104 years). The lack of such knowledge impedes our
ability to perform probabilistic seismic hazard assessments and understand the
underlying physics that controls repeated earthquake slip. In order to study the
existence of possible deficits or surpluses of geodetic and earthquake strain in the
Italian Apennines compared to 15 ±3 kyr multi-seismic-cycle strain-rates, horizontal
strain-rates are calculated using slip-vectors from striated faults and offsets of Late
Pleistocene-Holocene landforms and sediments, using an adaptation of the Kostrov
equations.
Strain-rates calculated over 15 ±3 kyr within 5km x 5km grid squares vary
from zero up to 2.34 ±0.54 x 10-7 yr-1, 3.69 ±1.33 x 10-8 yr-1, and 1.20 ±0.41
x 10-7 yr-1 in the central Apennines Lazio-Abruzzo region, the Molise-North
Campania region, and the southern Apennines South Campania-Basilicata region,
respectively, and resolve variations in strain orientations and magnitudes along the
strike of individual faults. Strain-rates over a time period of 15 ±3 kyrs from 5km x
5km grid squares integrated over an area of 1.28 x 104km2 (80 km x 160 km),
show the horizontal strain-rate of the central Apennines is 1.18 (+0.12/-0.04) x
10-8 yr-1 parallel to the regional principal strain direction (043-223o ±1o). In
Molise-North Campania, the horizontal principal strain-rate calculated over an area of 5 x
103 km2 (50 km x 100 km) is 2.11 (+1:14/-0:16) x 10-9 yr-1 along the principal
horizontal strain direction (039-219o ±3o). Within the southern Apennines region
with an area of 8 x 103 km2(50 km x 160 km), the average horizontal principal
strain-rate is 3.70 ±0:26 x 10-9 yr-1 along the horizontal principal strain direction
(044-224o ±2o).
Strain-rates calculated within 5 x 5 km and 20 x 20 km grid squares, and at a regional
scale, are highest in the central Apennines, medial in the southern Apennines and lowest
Molise-North Campania. At the regional length-scale, the strain-rates are comparable in
direction but smaller in magnitude to strain-rates calculated using GPS over 11 years and
earthquake moment tensors over 700 years (except in the central Apennines where long-term
strain-rates are comparable in magnitude to strain-rates calculated using historical
earthquakes). Smaller areas (~2000-7000 km2), corresponding to polygons defined by
geodesy campaigns (126 years) and seismic moment summations (700 years) show
higher 102 yr strain-rates than 104 yr strain-rates in some areas, with the opposite
situation in other areas where seismic moment release rates in large (> Ms 6.0)
magnitude historical earthquakes have been reported to be as low as zero. This
demonstrates that strain-rates vary spatially on the length-scales of 101-2km and on a
timescale between 101-2 yr and 104 yr in the Italian Apennines. The multi seismic
cycle strain-rates are used to calculate earthquake recurrence intervals for a given
earthquake slip magnitude, at the scale of individual seismic sources; these value
are compared to palaeoseismic data. The results are used to discuss spatial and
temporal earthquake clustering and the natural variability of the seismic cycle. |
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