New Insights into Seismic Sequences related to a Low Angle Normal Fault from a Seismic Catalog enhanced by Template Matching

Abstract:

The Alto Tiberina fault (ATF) system is dominated by a low-angle (dip < 30 deg) normal fault (LANF) with associated syn and antithetic high angle normal faults (splay faults) which are located in the hanging wall. Microseismicity (Ml < 2.4) was detected on the LANF, while several seismic sequences (Ml < 3.9, from 2012 to 2015) at shallow depth are related to the splay faults. The existence of several faults - showing heterogeneous spatio-temporal behavior during their seismic sequence - in combination with a dense seismometer array makes the study area a perfect real Earth laboratory. Furthermore historical data show that the region could host earthquakes with magnitudes of up to Mw 6.4. For a precise seismic hazard assessment, a detailed understanding of the seismicity is of importance.

In this study we use data from an array of borehole seismometers (part of The AltotiBerina near fault ObservatOry (TABOO)) deployed in the near field of the ATF, providing high quality and low noise seismic data. To extend an existing catalog we make use of a template matching algorithm to scan data from 2012 until 2015. We focus on the detection of small events and therefore use a frequency band between 5 to 50 Hz. Furthermore we only use templates, which satisfied a specific SNR threshold.

The resulting catalog provides a better time resolution than the preexisting one. Using this additional information we analyze the different seismic sequences with a focus on the temporal behavior to shed light into their physical properties (i.e. rupture patterns, seismicity recurrence intervals). Furthermore we are able to better resolve the temporal interplay between the microseismicity on the LANF and the seismic sequences on the splay faults. This information will help us to better understand the controversial slip behavior of LANFs.