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iPlex Lunch - spring-2016

The Parkfield tremors: slow and fast ruptures on the same asperity

April 6, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Sylvain Barbot - Earth Observatory of Singapore, NTU
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The Parkfield tremors: slow and fast ruptures on the same asperity

Investigation of Earthquake Rupture Dimension Through Seismic Wave Interferometry

April 13, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Aileen Zhang - UCLA
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Seminar Description coming soon.

Landscape evolution near the southeastern margin of the Tibetan Plateau

April 20, 2016
noon - 1 p.m.
Geology 1707

Presented By:

  • Devin McPhillips - USC
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Landscape evolution near the southeastern margin of the Tibetan Plateau: Surface uplift by lower-crustal flow?

Surface uplift on the diffuse southeastern margin of the Tibetan Plateau may result from flow of low-viscosity lower crust, rather than crustal shortening. In the absence of structural indicators, positive evidence for lower-crustal flow is limited. As a result, the incision of river gorges has become important proxy evidence for surface uplift. An ancient, low-relief landscape has previously served as a critical datum for measuring incision. Here, we investigate landscape evolution on the margin of the Plateau using a combination of geochronology and morphology. First, we present terrestrial cosmogenic nuclide (TCN) burial ages and low-temperature thermochronology from near the First Bend of the Yangtze River. We show that the rate of river incision likely declined near the end of the Miocene. This decline is not consistent with existing models of lower crustal flow, which suggest ongoing uplift and incision. This result is consistent with recent stable isotope paleoaltimetry, which indicates that the First Bend has persisted near its present elevation since at least middle Miocene time. Next, we present TCN erosion rates and morphometric data from four study sites extending ~500 km southeast of the Plateau margin. The results are complex, variously indicating river capture, local fault displacement, and regional surface uplift as the dominant drivers of river morphology. Locally, erosion rates and normalized steepness indices vary systematically with the mapped spatial extent of the paleolandscape. However, the landscape response to apparent paleolandscape uplift is remarkably muted in comparison with previous work from higher on the Plateau margin. In conclusion, we emphasize the complexity of landscape evolution southeast of the plateau margin. The mapped paleolandscape may not be a unique feature of regional extent. Detailed examination of landscape elements does not support the argument for lower-crustal flow as the primary driver of surface uplift, at least as currently formulated.

Acoustics of explosive volcanic eruptions

April 27, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Robin Matoza - UCSB
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Acoustics of explosive volcanic eruptions

Explosive volcanic eruptions can inject large volumes of ash into heavily travelled aviation routes and thus pose a significant societal and economic hazard. In remote volcanic regions, satellite data are sometimes the only technology available to observe volcanic eruptions and constrain ash-release parameters for aviation safety. Infrasound data fill this critical observational gap, providing ground-based data for remote volcanic eruptions. Infrasound is atmospheric sound with frequencies below 20 Hz, the lower frequency limit of human hearing. Explosive volcanic eruptions are among the most powerful sources of infrasound observed on Earth, with recordings routinely made at ranges of hundreds to thousands of kilometers. Significant advances in infrasonic data collection, signal processing methods, and propagation modeling have been achieved in the past two decades. Infrasound data can be exploited to detect, locate, and provide detailed chronologies of the timing of explosive eruptions for use in ash transport and dispersal models. This talk provides an overview of recent research progress on the source mechanisms of volcanic infrasound, the relation between volcanic infrasound and volcanic seismicity, the propagation of infrasound through atmospheric waveguides, and the automated detection, location, and cataloging of volcanic infrasound using global and regional infrasonic sensor networks.

Seismic Amplitudes from Ambient Noise Wavefront Tracking: Maps from USArray and Long Beach, and the

May 4, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Daniel Bowden - CALTECH
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Seismic Amplitudes from Ambient Noise Wavefront Tracking: Maps from USArray and Long Beach, and the Connection to Engineering Hazards

Tracking the wavefronts of Rayleigh waves through ambient noise has been demonstrated to reasonably recover site amplification terms across a very dense array in Long Beach, CA (0.5-1.5 sec periods) as well as the USArray (12-32 sec periods). The maps provide empirical observations of the relative strengths of Rayleigh waves, for a given period, laterally across both city and country scales. The methodology accounts for 2D propagation effects including attenuation, focusing and defocusing of the energy, and requires no assumptions about the structure at depth. Results correlate well with velocity models, and this provides an opportunity to test and understand shortcomings of both the models and method. We particularly focus on the tectonic and geologic structures that give rise to the observations, and the extent to which further 3D complexities such as topography and basin shape are represented in the amplifications. These measurements of surface waves are, however, fundamentally different from the site response terms traditionally estimated by vertically propagating waves in a 1D layered medium, and the relation between the two types of measurements is explored through comparisons of various datasets and simulations.

2011 Tohoku Tsunami Scattering and Wavefront Mapping from Offshore southern California Observations

May 11, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Monica Kohler - CALTECH
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2011 Tohoku Tsunami Scattering and Wavefront Mapping from Offshore southern California Observations

A wide spectrum of fault slip in multiple plate boundaries

May 18, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Abhijit Ghosh - UCR
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A wide spectrum of fault slip in multiple plate boundaries

Ray tracing forward modeling techniques and non-linear tomographic inversion

May 25, 2016
noon - 1 p.m.
Geology 1707

Presented By:

  • Zagid Abatchev - UCLA
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Ray tracing forward modeling techniques and non-linear tomographic inversion

Assessing the Depth of the Pacific Lithosphere-Asthenosphere Boundary From Various Proxies...

May 25, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Zheng Xing - UCLA
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Assessing the Depth of the Pacific Lithosphere-Asthenosphere Boundary From Various Proxies With a Bayesian Approach.

Autonomously Deployable Deep-ocean Seismic System - Communications Gateway for Ocean Observatories

June 1, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

  • Gabi laske - UCSD
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Autonomously Deployable Deep-ocean Seismic System - Communications Gateway for Ocean Observatories

In this talk, I describe an autonomously deployable, communications gateway designed to provide long-term and near real-time data from ocean observatories. The key features of this new system are its abilities to telemeter sensor data from the seafloor to shore without cables or moorings, and to be deployed without a ship, thereby greatly reducing life-cycle costs. The free-floating gateway uses a Liquid Robotics wave glider comprising a surfboard-sized float towed by a tethered, submerged glider, which converts wave motion into thrust. For navigation, the wave glider is equipped with a small computer, a GPS receiver, a rudder, solar panels and batteries, and an Iridium satellite modem. Acoustic communications connect the subsea instruments and the surface gateway while communications between the gateway and land are provided by the Iridium satellite constellation. Wave gliders have demonstrated trans-oceanic range and long-term station keeping capabilities. A shallow tow body houses a WHOI acoustic micro modem and a Benthos low frequency, directional transducer. A matching modem and transducer are mounted on the ocean bottom package. Tests of the surface gateway in 4350 m of water demonstrated an acoustic efficiency of approximately 396 bits/J. It has the ability to send 4 channels of compressed, 1 sample per second data from the ocean bottom to the gateway with an average power draw of approximately 0.15 W and a latency of less than 3 minutes. I present results from several short-term OBS tests off-shore La Jolla, at water depths of 1000 and nearly 4000 m. Ultimately, the package will be outfitted for two-year operations. Such data from presently unobserved ocean sites are critical for scientific research ranging from Earth structure to monitoring earthquakes and tsunami.