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iPlex Lunch - winter-2017

Robust Change Detection for Rapid Disaster Response using Synthetic Aperture Radar

Jan. 11, 2017
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Sang-Ho Yun - JPL
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With increasing number of spaceborne Synthetic Aperture Radar (SAR) missions, satellite SAR data are becoming useful for humanitarian applications. We used SAR data from the Italian Space Agency’s COSMO-SkyMed satellites and the Japan Aerospace Exploration Agency’s ALOS-1/2 satellites to produce damage proxy maps (maps showing areas of potential damage) of various disaster events, including February 2011 M6.4 Christchurch earthquake in New Zealand, the 2011 Kirishima volcano eruption in Kyushu, Japan, the 2013 Super Typhoon Haiyan, and the 2013 Moore Tornado in Oklahoma, United States. More recently, we responded to the April 25, 2015 M7.8 Gorkha earthquake in Nepal and January 2016 Midwest Floods along the Mississippi river in the U.S. The Gorkha earthquake caused more than 9,000 fatalities and widespread building damage in central Nepal. Four days after the earthquake, one of the COSMO-SkyMed satellites acquired SAR data over Kathmandu area. Nine days after the earthquake, the ALOS-2 SAR satellite covered larger area. Using these radar observations, we rapidly produced damage proxy maps derived from temporal changes in Interferometric SAR (InSAR) coherence. These maps were qualitatively validated through comparison with independent damage analyses by National Geospatial-Intelligence Agency (NGA) and the UNITAR’s (United Nations Institute for Training and Research’s) Operational Satellite Applications Programme (UNOSAT), and based on our own visual inspection of DigitalGlobe’s WorldView optical pre- vs. post-event imagery. Our maps were quickly released to responding agencies and the public, and used for damage assessment, determining inspection/imaging priorities, and reconnaissance fieldwork. Future response will become more rapid and reliable thanks to more SAR missions with open data policy, including the European Space Agency’s Sentinel-1A mission currently in operation and NASA’s NISAR mission planned to be launched in 2020.

What Lies Beneath? Vegetation and Mountain Interplay Determined by Coupled Cosmogenic Nuclide ...

Jan. 18, 2017
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Jane Willenbring - UCSD
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How important are the mountains for understanding forest patterns along elevation gradients. In this talk, I will describe a tropical forest laid upon an elevation gradient in a geomorphic disequilibrium to understand whether spatial patterns of slope and slope-dependent processes may cause nonlinear patterns of vegetation. The focus of the study is the upper Icacos River basin in the Luquillo Mountains, Puerto Rico ? a landscape currently adjusting through erosion to a 4-My-ago uplift event. These findings indicate that forest patterns on this tropical elevation gradient are strongly influenced by both climate and erosional controls driven by tectonics.

Why are slow earthquakes slow and what does chunky peanut butter have to do with it?

Jan. 25, 2017
noon - 12:50 p.m.
Geology 1707

Presented By:

  • An Yin - UCLA
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Why are slow earthquakes slow and what does chunky peanut butter have to do with it?

Deep (20-45 km) slow earthquakes are commonly referred to as slow-slip events (SSEs). They occur over durations of a few days to a few years with quasi-periodicities of weeks to years. Despite intense studies in the past decade, the physical control on recurring slow-slip events remains poorly understood. In this talk, I will present a new theoretical treatment that invokes a viscoplastic shear zone bounding an elastic overriding plate above and a rigid underthrusting plate below. The new model is inspired by the observation that quartzo-feldspathic mylonites that were formed at similar pressure and temperature conditions are composed of mixtures of cataclastically deformed feldspar and crystal-plastically deformed quartz. The mechanical property of such shear zones is similar to a chucky peanut butter: brittlely fragmented nuts embedded in an oily ductile medium; spreading the peanut butter (i.e., initiating viscous flow) requires the spreading force to exceed the yield strength of the peanut butter. Motion on such a shear zone, with a stepwise increase in yield strength due to shear-zone healing between slow-slip events, reproduces geodetically determined slow-slip histories. Comparing model predictions with observations yields key constraints on the rheological parameters of the subduction zones that host slow earthquakes.

Climatological Drivers of Plio-Pleistocene Pluvial Lakes in Western North America

Feb. 1, 2017
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Daniel Ibarra - Stanford
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Climatological Drivers of Plio-Pleistocene Pluvial Lakes in Western North America

Evidence for the persistence of large inland lakes in western North America during the Pliocene and Pleistocene provides first-order constraints on the regional water balance. In this talk I will discuss completed and ongoing work to investigate the climatological conditions driving lake levels in western North America during the mid-Pliocene warm period and Pleistocene glacial maxima. Geologic evidence suggests wet conditions persisted in this region during both periods despite dramatically different boundary conditions and pCO2 levels. I will present results of lake isotope mass balance modeling and compare them to climate model simulations of the Last Glacial Maximum (LGM) and mid-Pliocene produced by the Paleoclimate Modelling Intercomparison Project (PMIP and PlioMIP). Reduced evaporation and moderate increases in precipitation, relative to modern, led to moderate lake levels during the LGM. In contrast, larger precipitation increases may be the primary driver of lake levels during the Pliocene, suggesting a role for El Niño teleconnections during the mid-Pliocene.

Earthquake-driven erosion and mountain building

Feb. 8, 2017
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Gen Li - USC
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Earthquake-driven erosion and mountain building

Do earthquakes build or destroy mountain topography? Earthquakes are often thought to be a major driver of mountain uplift via repeated vertical displacements. But recent observations show that large earthquakes can erode mountains by inducing widespread landslides and enhancing riverine sediment export. The net effect of the competition between seismic uplift versus landslide-associated erosion remains to be quantitatively understood. Taking the 2008 Mw7.9 Wenchuan earthquake as a case study, we explore how earthquakes regulate the erosion and uplift of tectonically active mountain belts. Via landslide mapping and hydrological gauging, we quantify the erosion following the Wenchuan earthquake. Our results indicate that the Wenchuan landslide-induced erosion would counteract seismic uplift if all landslide debris is evacuated by rivers. We then derive long-term landslide rates over multiple earthquake cycles combining landslide volume models and earthquake return time statistics. We show that in our study area, landslide-associated erosion coincide spatially with the highest rates of long-term denudation, and that earthquake-induced landslides likely sustain the observed long-term orogenic denudation. These results demonstrate the significant erosive power of earthquakes and earthquake cycles. To compare landslide erosion with seismically induced uplift, we develop simple models of earthquake mass balance taking advantage of geophysical solutions to seismic and post-seismic deformations. We account for processes operating over complete earthquake cycles, including co-seismic deformation, post-seismic relaxation, landslide erosion and flexural-isostatic response to erosional unloading. The overall seismic mass balance is then discussed in the context of a new metric, the efficiency of topographic growth over earthquake cycles, which is found to be mainly controlled by co-seismic mass balance, landslide spatial pattern and the rheological property of the underlying lithosphere.

Erosion during mountain building: Insights from the southern Central Andes.

Feb. 15, 2017
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Pedro Val - UCSD
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Erosion during mountain building: Insights from the southern Central Andes.

The temporal evolution of erosion over million-year timescales is key to understand the development of mountain ranges and adjacent fold-and-thrust belts. Models of orogenic wedge dynamics predict an instantaneous response of erosion to pulses of rock uplift while stream-power based models predict that catchment-wide erosion maxima lag behind a pulse of rock uplift. Other models, empirical data, and global compilations of exhumation data demonstrate the dependency of denudation and rock exhumation rate on climate. However, site-specific studies suggest that these relationships can be diminished by tectonics. This talk will contain two case-studies from the southern Central Andes, one involving a temporal record of 10Be-derived paleoerosion rates from 8-3 Ma and another constraining the along-strike erosion rate pattern using 10Be and gauge data from both flanks of the Andes (Argentina and Chile). These case-studies support that the attainment of peak erosion rates is lagged with respect to the rock uplift pulse and that modern erosion rates are better explained by tectonics.

Climatic and geodynamic influences on ocean island geomorphology

Feb. 22, 2017
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Kim Huppert - MIT
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Climatic and geodynamic influences on ocean island geomorphology

With homogeneous bedrock, dramatic rainfall gradients, and remnant surfaces that constrain their age, initial topography, and vertical motions relative to sea level, volcanic ocean islands provide an exceptional natural experiment in landscape evolution. Analyses traversing gradients in island climate and bedrock age have the potential to advance our understanding of landscape evolution in a diverse range of continental settings. Yet, islands are initially conic, net subsiding, and boundary-dominated landmasses, in many ways dissimilar to most continental landscapes. In this talk, I examine unique aspects of island landscape evolution and exploit steep climate gradients and variations in bedrock age on volcanic ocean islands to quantify controls on erosion and constrain the contribution of lithosphere and mantle processes to surface deformation at hotspots. Through physically-based modeling, analysis of remote sensing and geochronologic data, and field measurements, I assess (1) the dominant mechanisms of vertical motion in the Hawaiian Islands, (2) the control of rainfall rates on the efficiency of bedrock river incision on the Hawaiian Island of Kaua’i, (3) the evolution of erosion rates over the course of landscape development on Kaua’i and other volcanic ocean islands, and (4) the mechanisms that cause volcanic ocean islands to subside below sea level to form atolls and guyots. These analyses provide empirical evidence for climatic control on erosion processes and they constrain the dynamics of plume-plate interactions at ocean hotspots.