Seismic mountain building: Landslides associated with the 2008 Wenchuan earthquake in the context of a generalized model for earthquake volume balance

Abstract

Here we assess earthquake volume balance and the growth of mountains in the context of a new landslide inventory for the M w 7.9 Wenchuan earthquake in central China. Coseismic landslides were mapped from high-resolution remote imagery using an automated algorithm and manual delineation, which allow us to distinguish clustered landslides that can bias landslide volume calculations. Employing a power-law landslide area-volume relation, we find that the volume of landslide-associated mass wasting ( 2.8 1 0.9/20.7 km 3 ) is lower than previously estimated ( 5.7-15.2 km 3 ) and comparable to the volume of rock uplift ( 2.6 6 1.2 km 3 ) during the Wenchuan earthquake. If fluvial evacuation removes landslide debris within the earthquake cycle, then the volume addition from coseismic uplift will be effectively offset by landslide erosion. If all earthquakes in the region followed this volume budget pattern, the efficient counteraction of coseismic rock uplift raises a fundamental question about how earthquakes build mountainous topography. To provide a framework for addressing this question, we explore a group of scaling relations to assess earthquake volume balance. We predict coseismic uplift volumes for thrust-fault earthquakes based on geophysical models for coseismic surface deformation and relations between fault rupture parameters and moment magnitude, M w . By coupling this scaling relation with landslide volume-M w scaling, we obtain an earthquake volume balance relation in terms of moment magnitude M w , which is consistent with the revised Wenchuan landslide volumes and observations from the 1999 Chi-Chi earthquake in Taiwan. Incorporating the Gutenburg-Richter frequency-M w relation, we use this volume balance to derive an analytical expression for crustal thickening from coseismic deformation based on an index of seismic intensity over a defined area. This model yields reasonable rates of crustal thickening from coseismic deformation (e.g., 0.1-0.5 km Ma 21 in tectonically active convergent settings), and implies that moderate magnitude earthquakes (M w 6-7) are likely responsible for most of the coseismic contribution to rock uplift because of their smaller landslide-associated volume reduction. Our first-order model does not consider a range of factors (e.g., lithology, climate conditions, epicentral depth, and tectonic setting), nor does it account for viscoelastic effects or isostatic responses to erosion, and there are important large uncertainties on the scaling relationships used to quantify coseismic deformation. Nevertheless, our study provides a conceptual framework and invites more rigorous modeling of seismic mountain building.

The control of earthquake sequences on hillslope stability

“…In addition to causing extensive socioeconomic disruption [Marano et al, 2010], earthquake-induced landslides play a key role in the evolution of mountain landscapes, increasing sediment flux through the fluvial network [Dadson et al, 2004;Hovius et al, 2011] and contributing to net erosion rates [Marc et al, 2015;Parker et al, 2011;Robinson et al, 2016]. While earthquake ground shaking triggers near-instantaneous landsliding [Li et al, 2014], some slopes do not fully fail and are weakened [Khattak et al, 2010], resulting in elevated susceptibility of hillslopes to landsliding during postseismic rainfall [Lin et al, 2008] and subsequent seismicity [Parker et al, 2015]. These legacy effects have been broadly attributed to landscape-scale weakening of hillslope substrates resulting from increased brittle (micro)fracturing and joint dilation ("damage") caused by transient hillslope stresses experienced during earthquake ground shaking [Wang et al, 2004].…”

Erosion Associated with Seismically-Induced Landslides in the Middle Longmen Shan Region, Eastern Tibetan Plateau, China

“…We also compare the amount of erosion obtained from the differential DEM method with previous results of landslide volumes proposed by Li et al [11].…”

“…In this study, we estimated the seismically-induced erosion associated with landslides using the DEM differential method [26] and the landslide volume information from Li et al [11].…”

“…There is a consensus that the Yingxiu-Beichuan and Guanxian-Anxian faults are the seismogenic faults associated with the 2008 Wenchuan earthquake [16][17][18]. Numerous co-seismic landslides were triggered due to the co-seismic deformation and strong ground motion along the rupture zone [4,11,25,39,40], influencing the local erosion rate as well as the topographic evolution.…”

“…The 2008 Mw 7.9 Wenchuan earthquake triggered numerous landslides, and provided a rare opportunity to study the geomorphic response to a strong earthquake ( Figure 1). Due to the limitation of available data in previous studies, landslide volumes have typically been derived from landslide areas using statistical equations [4,[10][11][12][13]. Researchers also tried using the spaceborne interferometric synthetic aperture radar (InSAR) [14] and remote sensing and digital terrain model (DTM) data [15] to evaluate mass wasting volume, but only concentrated on the giant Daguangbao [16][17][18].…”