Soft-sediment deformation structures interpreted as seismites in lacustrine sediments of the Prebetic Zone, SE Spain, and their potential use as indicators of earthquake magnitudes during the Late Miocene

Abstract

Lacustrine formations of Late Miocene age in the Prebetic area, SE Spain, show several types of deformational structures that are interpreted as seismites. They are present in both marginal and deep lacustrine facies. Seismites formed in marginal lake environments comprise sand dikes, pillows and intruded and fractured gravels. In deep lacustrine facies, the seismites are represented by pseudonodules, mushroom-like silts protruding into laminites, mixed layers, disturbed varved lamination and loop bedding. The measured orientations of these structures are consistent with the orientations of the main faults limiting the basins, showing that their origin is clearly related to the tectonic stress field that prevailed in the region during the Late Miocene. The magnitudes of the earthquakes that deformed the sediments have been estimated after published data from both ancient and recent lake deposits accumulated in tectonic active regions elsewhere. A rank of earthquake magnitudes with two end-members, i.e. the lowest magnitudes recorded by loop bedding in laminites and the highest magnitudes represented by intruded and fractured gravels, is proposed.

Active tectonics in Eastern Lunana (NW Bhutan): Implications for the seismic and glacial hazard potential of the Bhutan Himalaya

“…[21] Seismically induced liquefaction causes a volume decrease within the source bed of the liquefied layer, which can result in the development of normal faults in the overlying sediments [e.g., Rodriguez-Pascua et al, 2000;Rossetti and Góes, 2000;Moretti, 2000]. We suggest this mechanism as the cause for complex convolute folding and normal faulting within the Tshojo sediments and expect escaping water-sediment mixtures from the liquefied source bed to be responsible for the adjacent sand injections ( Figure 7).…”

Origins of Soft-Sediment Deformation Structures from the Batang Paleodammed Lakes in the Upper Jinsha River, SE Tibetan Plateau

“…The origin of similar structures in lacustrine deposits has been attributed to an elastic-plastic response of sediment to shear-stress caused by the back and forth movement of water [15,44]. The ball-and-pillow structures ( Figure 5) is a type of load structure, and may form as a consequence of loading of a denser sand layer over a less dense clayey silt layer during earthquake induced liquefaction, so that fine sands would fall into the clayey silt layer in a pillow or globular shape [45].…”

The Traces of Earthquake (Seismites): Examples from Lake Van Deposits (Turkey)

“…Ball and pillow structures occur with liquefaction of unconsolidated sediments. Because of the seismic tremors, liquefied sand size sediments are merged each other and create a balllike structure (Montenat et al, 1987;Ringrose, 1989;Cojan & Thiry, 1992;Rodriguez-Pascua et al, 2000).…”

“…The most known occurence of soft sediment deformation structures are overpressure of sediments (Lowe & LoPiccolo, 1974;Lowe, 1975), storm waves (Molina et al, 1998;Alfaro et al, 2002) and seismic shakings (Seilacher, 1969;Lowe, 1975;Sims, 1975;Rossetti, 1999;Vanneste et al, 1999;Jones & Omoto, 2000;Rodriguez-Pascua et al, 2000;Bowman et al, 2004). Deformation structures in lacustrine deposits of Lake Van were evaluated in the light of these trigger mechanism.…”