The relationship between coastal uplift and normal faulting in the Mejillones Peninsula Northern Chile: the control of the subduction earthquake cycle

Abstract:

The Mejillones Peninsula lies directly above the seismogenic zone, which marks the shallow coupled part of the Nazca and South America plates. In this peninsula uplifted abrasion platforms and normal faults constitute spectacular evidences for Quaternary tectonics. In this contribution we presented new data about the age of marine abrasion platforms and fault slip rates based on cosmogenic nuclides ages, tephra geochronology and OSL ages. We mapped the net offset related to two regional scale normal faults (Mejillones Fault and Caleta Herradura Fault), which control the topography of the Mejillones Peninsula. In general we observed that the altitude of the abrasion platforms is strongly influenced by normal fault offset and that slip rate varies systematically with respect to the strike of the normal faults. In fact along-strike variation in the amount of normal-fault slip along these two faults has determined the present position of marine abrasion platforms preserved in two north-south regional scale horst structures. We determined that Quaternary slip variation along strike of the Mejillones Faults increase northward and a tip-point-fault can be identified in the central part of the Mejillones Peninsula. At the same latitude the Caleta Herradura Fault displaces identical stratigraphic markers than the Mejillones Fault and the net-fault slip is similar to the northern section of the Mejillones Fault. It indicates that normal fault offset is transferred from one structure to the other and that both faults are interlink structures producing near the same amount of E-W finite extension across this Peninsula. Analytical modeling shows that upper plate extension is promoted during the propagation of subduction earthquakes beneath the Mejillones Peninsula. The uplift of the peninsula is counterbalanced during the interseismic and coseismic phase of subduction earthquake cycle depending on the extent of earthquake ruptures down-dip of the plate interface.