Geometry and evolution of a fault‐controlled Quaternary basin by means of TDEM and single‐station ambient vibration surveys: The example of the 2009 L'Aquila earthquake area, central Italy

Abstract

We applied a joint survey approach integrating time domain electromagnetic soundings and single‐station ambient vibration surveys in the Middle Aterno Valley (MAV), an intermontane basin in central Italy and the locus of the 2009 L'Aquila earthquake. By imaging the buried interface between the infilling deposits and the top of the pre‐Quaternary bedrock, we reveal the 3‐D basin geometry and gain insights into the long‐term basin evolution. We reconstruct a complex subsurface architecture, characterized by three main depocenters separated by thresholds. Basin infill thickness varies from ~200–300 m in the north to more than 450 m to the southeast. Our subsurface model indicates a strong structural control on the architecture of the basin and highlights that the MAV experienced considerable modifications in its configuration over time. The buried shape of the MAV suggests a recent and still ongoing predominant tectonic control by the NW‐SE trending Paganica‐San Demetrio Fault System (PSDFS), which crosscuts older ~ENE and NNE trending extensional faults. Furthermore, we postulate that the present‐day arrangement of the PSDFS is the result of the linkage of two previously isolated fault segments. We provide constraints on the location of the southeastern boundary of the PSDFS, defining an overall ~19 km long fault system characterized by a considerable seismogenetic potential and a maximum expected magnitude larger than M 6.5. This study emphasizes the benefit of combining two easily deployable geophysical methods for reconstructing the 3‐D geometry of a tectonically controlled basin. Our joint approach provided us with a consistent match between these two independent estimations of the basin substratum depth within 15%.

Geometry and Structure of a Fault‐Bounded Extensional Basin by Integrating Geophysical Surveys and Seismic Anisotropy Across the 30 October 2016 Mw 6.5 Earthquake Fault (Central Italy): The Pian Grande di Castelluccio Basin

“…No direct measurements of V S are available within the PGC basin, so we describe the spatial change of f 0 as compared to top bedrock depth estimates from adjacent TDEM soundings in a qualitative way. Average V S values spanning ~500–900 m/s for the sedimentary infill of PGC are likely, as suggested by local geology, shallow borehole stratigraphy (see section 4) and also by ongoing studies in the same area and past works carried out in other similar basins of the central Apennines (Civico et al, ; Di Giulio et al, , ; MS–AQ Working Group, ).…”

“…It is widely used to image the electrical properties of subsurface geological structures over different lithological settings with the capability to reach significant penetration depths over moderately resistive environments (few hundreds of meters; Bedrosian et al, ). We follow the approach by Civico et al () to map the top bedrock depths using 1‐D vertical resistivity models. We acquired 13 TDEM soundings both with central‐loop and offset receiver configurations using a 50‐m transmitter loop size along two transects (A‐A ' and B‐B′ in Figure ).…”

“…Subsequent works in the same area highlighted the successfulness of a multidisciplinary approach. Villani, Tulliani et al (), Villani, Pucci et al (), Villani et al (), and Civico et al () combined different near‐surface geophysical techniques such as high‐resolution refraction tomography, electrical resistivity tomography (ERT), magnetometry, time domain electromagnetic measurements (TDEM), and ambient vibration recordings calibrated with detailed geological data, trenches, and boreholes to image fault zones and to map the top bedrock surface of fault‐controlled basins. The geophysical imaging of these active faults revealed some common features of their extensional hangingwall basins: (1) regardless of their size, the basins are not flat bottomed, rather display complex topography and abrupt elevation changes at different spatial wavelengths; (2) the large‐scale basin shape is primarily controlled by normal faults, sometimes buried by recent clastic cover (depending on the competition between rates of sedimentation and fault slip); (3) the retrieved subsurface faults are hierarchically nested, and consist of a principal (a few meters to several tens of meters wide) deformation zone that accommodates most of the displacement (master fault), paired with several subsidiary splays; (4) such splays form a kinematically coherent fault system, and they may rupture the surface during strong ( M > 6) earthquakes; (5) the overall width of the extensional deformation zone ranges from a few hundred meters to nearly 3–5 km as a function of the degree of fault maturity and the length of the active fault system.…”

“…To fill this information gap, we combined different geophysical techniques: in particular, we performed ERT and TDEM measurements coupled with ambient vibrations recordings along a survey transect running approximately E‐W across the PGC basin. We follow the multidisciplinary approach adopted by Civico et al (), and we include some additional analyses. In fact, to further constrain the deep structural setting of the basin and the pattern of fractures, we investigated the seismic anisotropy, by analyzing small earthquakes recorded during the surveys.…”

Transient Electromagnetic Investigations in a Tectonic Domain of the Kachchh Intraplate Region, Western India: A Morphotectonic Study of the Kachchh Mainland Fault

“…Deng and Zhang () showed that active reverse faulting also generates colluvial wedges during a reverse faulting earthquakes and may also be used to identify reverse faulting earthquake events and in turn to analyze the paleo‐earthquake history. Shallow geophysical methods, in particular electrical resistivity studies, have become a successful practice in imaging fault zones, their attributes in a variety of geological settings, and image colluvial wedges/earthquake‐related structures (Buddensiek et al, ; Civico et al, ; Hanafy, ; Mattson, ; Maurya et al, ; Morey & Schuster, ; Ostrowski et al, ; Patidar et al, ; Pavan Kumar, Mahesh, et al, ; Sheley et al, ; Villani et al, ). In the present study, we carried out transient electromagnetic (TEM) investigations across the KMF zone (Figure ) to image the primary fault along with associated splays for better understanding the geometry of the fault zone.…”