Seismic Triggering Mechanisms of Large–scale Landslides, Valles Marineris

Large–scale landslides in Valles Marineris wallrock are analyzed in order to determine what triggering mechanisms caused the landslides. These landslides occur in the locality of large faults, and therefore it is hypothesized that the landslides are the result of marsquakes triggering slope instability. This work confirms that landslides occur where the seismic hazard map forecasts highest seismic slide potential. Introduction: To demonstrate the mechanics of large–scale Martian slides this study quantifies the magnitude of marsquakes and resulting ground motions based on terrestrial methods [1–9]. Additionally, computer modeling with XSTABL [10] is used to establish ground motion needed to induce failure of Martian slopes where previous landslides have occurred. These analyses demonstrate that faults in and around Valles Marineris are large enough to generate significant ground motions that can induce landslides (Fig. 1). Results: Large paleolandslides on Earth are the result of large earthquakes and have been shown to correspond with earthquake magnitude and distance from the epicenter (Fig. 2) [1, 2]. Surface expression of fault lengths over 100 km is not uncommon in and around Valles Marineris, and as a result these faults are capable of producing quakes in excess of magnitude 8 (Fig. 2) [3]. Calculations of Arias intensity [4] ground accelerations as a result of marsquakes, reveals that marsquakes can cause ground accelerations of 0.5 m/s within 10 km of the epicenter. Mars Orbiting Laser Altimeter (MOLA) data digital elevation models were created in Arcview GIS for Valles Marineris to define slope height and angle throughout the chasmata. Furthermore, a digital geologic map was produced based on previous geologic interpretations [13, 14, 15] in order to identify faults and define seismic response of surficial materials [7, 8, 11, 12]. By digitally measuring the surface length of faults, maximum potential marsquake magnitudes are defined for all large faults in Valles Marineris because the length of fault is directly related to the maximum possible quake that can occur on that fault [6]. Additionally, seismic models were constrained by fault type as defined on previous geologic maps [13, 14, 15] using GIS to modify seismic motion mo dels for direction of fault motion (Fig. 2). Fig. 1. The maximum distance that landslides can occur from the epicenter of an earthquake is based on an historical data set of 30 earthquakes (after Keefer, 1984).