Summary The Pollino range is a region of slow deformation where earthquakes generally nucleate on low-angle normal faults. Recent studies have mapped fault structures and identified fluid-related dynamics responsible for historical and recent seismicity in the area. Here, we apply the coda-normalization method at multiple frequencies and scales to image the 3D P-wave attenuation (QP) properties of its slowly-deforming fault network. The wide-scale average attenuation properties of the Pollino range are typical for a stable continental block, with a dependence of QP on frequency of $Q_P^{-1}=(0.0011\pm 0.0008) f^{(0.36\pm 0.32)}$. Using only waveforms comprised in the area of seismic swarms, the dependence of attenuation on frequency increases ($Q_P^{-1}=(0.0373\pm 0.0011) f^{(-0.59\pm 0.01)}$), as expected when targeting seismically-active faults. A shallow very-low-attenuation anomaly (max depth of 4-5 km) caps the seismicity recorded within the western cluster 1 of the Pollino seismic sequence (2012, maximum magnitude MW = 5.1). High-attenuation volumes below this anomaly are likely related to fluid storage and comprise the western and northern portions of cluster 1 and the Mercure basin. These anomalies are constrained to the NW by a sharp low-attenuation interface, corresponding to the transition towards the eastern unit of the Apennine Platform under the Lauria mountains. The low-seismicity volume between cluster 1 and cluster 2 (maximum magnitude MW = 4.3, east of the primary) shows diffuse low-to-average attenuation features. There is no clear indication of fluid-filled pathways between the two clusters resolvable at our resolution. In this volume, the attenuation values are anyway lower than in recognized low-attenuation blocks, like the Lauria Mountain and Pollino Range. As the volume develops in a region marked at surface by small-scale cross-faulting, it suggests no actual barrier between clusters, more likely a system of small locked fault patches that can break in the future. Our model loses resolution at depth, but it can still resolve a 5-to-15-km-deep high-attenuation anomaly that underlies the Castrovillari basin. This anomaly is an ideal deep source for the SE-to-NW migration of historical seismicity. Our novel deep structural maps support the hypothesis that the Pollino sequence has been caused by a mechanism of deep and lateral fluid-induced migration.

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<p>Seismic waves lose energy during propagation in heterogeneous Earth media. Their decrease of amplitude, defined as seismic attenuation, is central in the description of seismic wave propagation. The attenuation of coherent waves can be described by the total quality factor, <em>Q</em>, and it is defined as the fractional energy lost per cycle, controlling the decay of the energy density spectrum with lapse time. The coda normalization (CN) method is a method to measure the attenuation of P- or S-waves by taking the ratio of the direct wave energy and late coda wave energy in order to remove the source and site effects from P- and S-wave spectra. One of the main assumptions of the CN method is that coda attenuation, i.e. the decay of coda energy with lapse time measured by the coda quality factor <em>Q<sub>c</sub></em> is constant. However, several studies showed that Q<sub>c</sub> is not uniform in the crust for the lapse times considered in most attenuation studies. In this work, we propose a method to overcome this assumption, measuring coda attenuation for each source-station path and evaluating the effect of different scattering regimes on the corresponding imaging. The data consists of passive waveforms from the fault network in the Pollino Area (Southern Italy) and Mount St. Helens volcano (USA).</p>

<p>The North Anatolian Fault (NAF) is a right-lateral, strike-slip fault in the northern part of the Anatolian peninsula. It is estimated to have a length of up to 1500 km, extending westwards between the Karliova Triple Junction, where it nucleates, to the Aegean Sea. In the west and close to the Sea of Marmara, the NAF splays into northern (NNAF) and southern (SNAF) strands. The splay of the western part of the NAF separates the area into three primary terranes: the Istanbul Zone (north of the northern strand), the Armutlu-Almacik Block (between the two strands of the fault) and the Sakarya Zone (south of the southern strand).</p><p>There have been a series of high-magnitude earthquakes along the NAF since the 1930s, migrating from east to west. In order to investigate the western part of the North Anatolian Fault Zone (NAFZ), which is the most seismically active at the moment, the Dense Array for North Anatolia (DANA) temporary seismic network was deployed for 18 months between 2012 and 2013. A set of local earthquakes, recorded by DANA, were utilised to study the 2D scattering and coda attenuation structure in the western NAFZ, between 1 and 18 Hz. P-wave arrival times were manually picked and the events were re-located using the Non-Linear Location software. Peak-delay travel times were calculated as a measure of forward scattering, and the exponential decay of the coda wave envelopes was used to invert for the absorption structure using multiple scattering sensitivity kernels.</p><p>The obtained models are 2D averages of the first 10-15 km of the crust, where the majority of the seismic activity is located and they have been compared to recent geophysical studies in the same area. The scattering structure, between 1 and 6 Hz, highlights the three main tectonic units in the area. The absorption structure is generally more heterogeneous than the scattering structure, with the overall absorption decreasing as the frequency increases. The lithological variations and heterogeneity between and within the three terranes of the area, arising from the complex tectonic history of the region, are believed to be the main reasons for the scattering and absorption observations made. The high absorption zones observed along the two branches of the fault, and especially the southern branch, is a very important finding, as the signature of the southern branch in geophysical studies is often unclear.</p>