Mechanisms of earthquake induced chemical and fluid transport to carbonate groundwater springs after earthquakes

Mechanisms by which hydrochemical changes occur after earthquakes are not well documented. We use the 2016-2017 central Italy seismic sequence, which caused notable hydrochemical transient variations in groundwater springs to address this topic, with special reference to effects on fractured carbonate aquifers. Hydrochemistry measured before and after the earthquakes at four springs at varying distances from the epicenters all showed immediate post-mainshock peaks in trace element concentrations, but little change in major elements. Most parameters returned to pre-earthquake values before the last events of the seismic sequence. The source of solutes, particularly trace elements, is longer residence time pore water stored in slow moving fractures or abandoned karstic flowpaths. These fluids were expelled into the main flow paths after an increase in pore pressure, hydraulic conductivity, and shaking from co-seismic aquifer stress. The weak response to the later earthquakes is explained by progressive depletion of high solute fluids as earlier shocks flushed out the stored fluids in the fractures. Spring \u3b413CDIC values closest to a deep magma source to the west became enriched relative to pre-earthquake values following the August 24th event. This enrichment indicates input from deeply-sourced dissolved CO2 gas after dilation of specific fault conduits. Differences in carbon isotopic responses between springs are attributed to proximity to the deep CO2 source. Most of the transient chemical changes seen in the three fractured carbonate aquifers are attributed to local shaking and emptying of isolated pores and fractures, and are not from rapid upward movement of deep fluids

Faults geometry and the role of fluids in the 2016-2017 Central Italy seismic sequence

The 2016–2017 Central Italy seismic sequence ruptured overlapping normal faults of the Apennines mountain chain, in nine earthquakes with magnitude Mw > 5 within a few months. Here we investigate the structure of the fault system using an extensive aftershock data set, from joint permanent and temporary seismic networks, and 3‐D Vp and Vp/Vs velocity models. We show that mainshocks nucleated on gently west dipping planes that we interpret as inverted steep ramps inherited from the late Pliocene compression. The two large shocks, the 24 August, Mw = 6.0 Amatrice and the 30 October, Mw = 6.5 Norcia occurred on distinct faults reactivated by high pore pressure at the footwall, as indicated by positive Vp/Vs anomalies. The lateral extent of the overpressurized volume includes the fault patch of the Norcia earthquake. The irregular geometry of normal faults together with the reactivated ramps leads to the kinematic complexity observed during the coseismic ruptures and the spatial distribution of aftershocks

Geometry and kinematics of Triassic-to-Recent structures in the Northern-Central Apennines: a review and an original working hypothesis

The geological evolution of the Northern-Central Apennines has been strongly controlled by structural features inherited from pre-thrusting stages. The Apennines consist of a fold-and-thrust belt developed during Neogene time, involving sedimentary successions that were deposited within different paleogeographic domains. The paleogeographic evolution was controlled by the effects of syn-sedimentary tectonics that were active in the Triassic-Neogene time interval, and that are, from Trias to Neogene, related to different geodynamic settings. The Jurassic extensional phase favoured the dissecting of the Triassic carbonate platform and led to the development of different paleogeographic domains. Main oblique and trasversal faults, with transtensive kinematics, characterized the boundaries between different domains. After the Jurassic phase, from Cretaceous to Neogene, the Northern-Central Apennines were characterized by the development of ridges and depressions. These structures were affected by the development of normal fault systems, bending processes within the ridges, with uplift of the crestal sectors and tilting in the peripheripheral ones. The geometries and the structural setting of the foreland domains, of the foredeep and piggy back basins and of the Neogene Apenninic thrust belt are controlled by evolution of the former tectonic elements evolution. The development of extensional faults, the uplift and bending observed in the Apenninic sedimentary sequences during the convergence phase and during a part of the continental collision phase could represent distal effect of the dominant compressional regime. In this geodynamic domain the first tectonic inversion processes in a positive sense occurred along the pre-existing Jurassic listric faults systems. The reactivation first affected the flat sectors of the fault planes and then progressively more superficial ones. In the upper sedimentary cover these processes favoured buckling, flexuring and faulting. Furthermore, during the subsequent involvement of the foreland domains in the foredeep and chain systems, the propagating thrust surface still reused former discontinuities both as a frontal and lateral ramp, completely inverting their movement. During the compressional stage the west-dipping listric normal faults were reactivated in positive sense. The former east-dipping normal faults have been eastward rotated or offset by thrust faults

Guida all’escursione: Geologia e geomorfologia del settore fermano nel bacino periadriatico marchigiano-abruzzese.

Here we have a brief description of geology and geomorphology character of Plio-pleistocene lands of Ascoli Province (AP) and relative summary of third day field trip of the 3 rd Geology and Information Technologies Group Congress, held in Offida, Italy, from 3 rd to 5 th of June 2008. We describe Neogene-Pleistocenic periadriatic sector evolution, sequence of events and geomorphologic character of Southern-central Marche highlands