62. Howe, T. C., and P. Bird [2010] Exploratory models of
long-term crustal flow and resulting seismicity in the Alpine-Aegean orogen, *Tectonics,
29*, TC4023, doi: 10.1029/2009TC002565.

**Abstract**. Long-term
crustal flow is computed with a kinematic finite-element model based on
iterated weighted-least-squares fits to data and prior constraints. Data
include 773 fault traces, 106 fault offset rates, 510 geodetic velocities, 2566
principal stress azimuths, and velocity boundary conditions representing the
rigid parts of the Eurasia, Africa, and Anatolia plates. Model predictions
include long-term velocities, fault slip rates, and distributed permanent
strain rates between faults. One model assumes that geodetic velocities
measured adjacent to the Aegean Trench reflect a temporarily-locked subduction
zone; in this case long-term subduction velocity averages 45 mm/a and rapid
crustal extension is predicted in the southern Aegean Sea. Another model
assumes steady creeping subduction; in this case subduction velocity averages
only 29 mm/a and the eastern Aegean Sea floor is predicted to be more nearly
rigid. Long-term seismicity maps are computed for each model, based on the
SHIFT hypotheses and previous global calibrations of plate-boundary earthquake
production. Retrospective comparisons to seismic catalogs are encouraging: map
patterns, spatial distribution functions, and total earthquake counts are all
comparable. While neither model accurately predicts earthquake rates at all
magnitudes, the creeping-subduction model is more accurate for strong *m*6+
events, which dominate the seismic hazard.

Input and output files for/from neotectonic modeling of the Alpine-Aegean orogen

Long_Term_Seismicity software for long-term seismicity forecasts

Long-term seismicity forecast of shallow earthquakes in the Alpine-Aegean region

Figure 1. Traces of active and potentially-active faults within the Alpine-Aegean orogen (heavy grey outline) included in modeling. Dip ticks indicate nominal senses of slip, but faults lacking geologic offset rates are free to slip with opposite sense. Polyconic projection.

Figure 2. GPS velocities selected
from literature, with 90%-confidence ellipses. Velocity is extrapolated
forward for 10^{7} years. Some benchmark codes omitted for clarity.

Figure 3. Azimuths of the
most-compressive horizontal principal stress direction, as interpolated by
NeoKinema using the clustered-data method of *Bird & Li* [1996].
Symbols are omitted if 90%-confidence sectors (not shown) are broader than
±45°. For clarity, only 1/4 of interpolated directions are plotted.

Figure 4. Root-mean-square
misfits (dimensionless measures, defined in equations 2-4) of NeoKinema models, as functions
of dimensional weight parameters *L*_{0} and *A*_{0}
(defined in text). Unsuccessful models with sup(*N*_{2}) > 2.2
are shown by solid triangles, successful model in regular grid-search is shown
by gray square, and the preferred model is shown by open hexagon.

Figure 5. Long-term-average
velocity fields of the seismic subduction model (left) and the creeping
subduction model (right). Velocity vectors are extrapolated forward for 10^{7}
years. For clarity, only 1/9 of computed nodal velocities are plotted as
vectors. Contour interval of shading is 1 mm/a. Velocity reference frame is
stable Eurasia to the north.

Figure 6. Fault heave rates predicted by the seismic subduction model (left) and the creeping subduction model (right). Faults with oblique slip are represented by two superposed colored ribbons. Note that the seismic subduction model predicts both faster subduction (blue bands) and faster extension (yellow traces) in the southern Aegean Sea.

Figure 7. Long-term rates of
shallow (< 70 km) seismicity for magnitudes *m* > 5 forecast by the
seismic subduction model (left) and the creeping subduction model (right).
Epicenters (identical in both frames) are of shallow *m* > 5
earthquakes from the Global Centroid Moment Tensor catalog, 1977-2008.

Figure 8. Spatial distribution
functions (SDFs, defined in text) for the seismic subduction model (top left)
and the creeping subduction model (top right). Each plot in top row shows both
forecast and actual seismicity, both as functions of cumulative area. Bottom
row shows cross-plots of actual SDFs as a function of forecast SDFs; here the
ideal is a diagonal line (dashed line). For threshold *m* > 5, actual
seismicity is less than forecast by the seismic-subduction model but more than
forecast by the creeping-subduction model; in each case the discrepancy occurs in
the forecast high-seismicity areas (right part of each graph). The shift to a
preference for the creeping-subduction model as threshold magnitude is raised
above 5 is shown in Table 1.