QuickTime Movies: Exploring the Spatial Extent of Aftershocks from the 2001 and 2005 Anza sequences
We explore the spatial footprint of aftershocks from the 2005 and
2001 Anza mainshocks, which had magnitudes of 5.2 and 5.1,
respectively. For each sequence, we use the first 2 days of data to
create two data sets. The first includes all cataloged aftershocks
within the sequence and the second includes only the larger magnitude
aftershocks (magnitude 2 and above). The purpose of presenting the
data in this way is to show that the spatial extent of the aftershock
zone is substantially reduced for catalogs that only track larger
magnitude aftershocks. Based on all available data the Anza
aftershock zones span ~50 km, whereas using only the larger magnitude
events the spatial extent of the aftershocks is only ~5 km. We
conclude that the size of an aftershock zone can appear misleadingly
small if there is not substantial effort spent in cataloging small
magnitude aftershocks using data recorded by robust seismic networks
close to the source region.
These movies show the temporal evolution of the first 48 hours of the
2001 and 2005 aftershock sequences (current time is marked in red and
past time is marked in yellow on the lower timebar).
Aftershocks in the current time window are represented as red
circles, which are then marked as yellow points as time progresses.
For reference we include concentric circles about the epicenter that
extend out to a 70 km radius (140 km diameter) in increments of 10
km. Known fault traces (black lines) and select town locations
(labeled triangular markers) are also included.
Movies:
Temporal Evolution of the 2001 Sequence, all aftershocks (499 earthquakes; movie size 7.6 MB)
Temporal Evolution of the 2001 Sequence, M>2 (15 earthquakes; movie size 7.5 MB)
Temporal Evolution of the 2005 Sequence, all aftershocks (1615 earthquakes; movie size 7.6 MB)
Temporal Evolution of the 2005 Sequence, M>2 (25 earthquakes; movie size 7.5 MB)
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