Abstract:
Clastic dikes are often the only evidence of past disasters in poorly exposed areas and therefore their findings are extremely important for earthquake study. However, the variety of their origins greatly complicates the use of clastic dikes to assess the seismic hazards within the manifold environments. This paper systematizes main triggers, formation mechanisms and some matching indicative features of tabular and cylindrical bodies with an emphasis on the importance of revealing the injection dikes formed by fluidized injection of clastic material into the host sedimentary layers (from the bottom upwards) and associated with overpressure buildup and hydraulic fracturing. Based on the revision of known seismic liquefaction features and specific descriptions of the injection dikes, this overview defines 12 general and 12 individual geological and structural criteria (for study in sectional view), which make it possible to establish confidently the earthquake origin of the dikes caused by fluidization from seismic liquefaction. In addition, ground penetrating radar data correlating with trenching suggest indicative searching criteria of the injection dikes on radargrams, namely: a pipe-shaped anomaly or a composite anomaly combining a tubular form in the lower part with an isometric in the upper [i]; relatively high values of unipolar positive echoes on the trace of GPR signal [ii]; an occurrence of the same anomaly on adjacent parallel profiles located the first tens of meters apart [iii]; and stratigraphic disruptions of the radar events on the background of their continuous horizontal position [iv]. Finally, the paper illustrates that the clastic dikes can be successfully applied to determine the age and the recurrence interval, the epicenter location and a lower-bound magnitude/intensity of paleoearthquakes, thus providing geological data for seismic hazard assessments in the regions, in which unconsolidated deposits capable to liquefaction are common.
