iPlex Lunch - fall-2013
Seismic constraints on the structure and deformation of continental lithosphere
Oct. 9, 2013
noon - 1 p.m.
Geology 1707
Presented By:
See Event on Google.Subscribe to Calendar
Seminar Description coming soon.
Iron-rich oxides at Earth's core-mantle boundary
Oct. 16, 2013
noon - 1 p.m.
Geology 1707
Presented By:
See Event on Google.Subscribe to Calendar
Seminar Description coming soon.
Constraints on the oceanic lithosphere-asthenosphere boundary/Constraining global radial anisotropy
Oct. 23, 2013
noon - 1 p.m.
Geology 1707
Presented By:
- Kaiqing Yuan - UCLA
- Zheng Xing - UCLA
Subscribe to Calendar
Kaiqing Yuan (UCLA) “Constraints on the oceanic lithosphere-asthenosphere boundary from seismic anisotropy”
Zheng Xing (UCLA) “Constraining global radial anisotropy in the upper mantle”
Rate-and-state Coulomb stress-based earthquake forecasts
Oct. 30, 2013
noon - 1 p.m.
Geology 1707
Presented By:
- Anne Strader - UCLA
Subscribe to Calendar
Seminar Description coming soon.
Looking for aseismic slip associated with small earthquakes using strain and seismic data
Nov. 6, 2013
noon - 1 p.m.
Geology 1707
Presented By:
See Event on Google.Subscribe to Calendar
We take two approaches to investigating aseismic slip associated with small earthquakes. First, we note that the recurrence intervals of repeating earthquakes raise the possibility that much of the slip associated with small events is aseismic. To test this hypothesis, we examine the strain changes associated with M2 to 4 earthquakes near San Juan Bautista, CA. We bin the earthquakes into 3 to 5 groups according to their magnitude. We then invert for an average time history of strain per seismic moment for each group. Each of the estimated strain time series displays a step at the time of the earthquakes. If we assume that the seismic moment scales as 10^(1.0M), the ratio of the strain step to seismic moment is approximately constant with magnitude. This would imply that the ratio of aseismic to seismic slip is approximately constant with magnitude. In a second approach to looking for aseismic slip, we present a phase coherence approach to investigate emergent seismic precursors to earthquakes. This method allows us to identify seismic signals coming from the earthquake location, even if those signals have complicated source-time functions. We confirm that a precursor to a M3.9 event in Nenana, AK originates near the earthquake location. Initial investigation of events on the San Jacinto Fault reveal no systematically occurring precursors.
High frequency seismic wave in the slab beneath Italy and its implication
Nov. 20, 2013
noon - 1 p.m.
Geology 1707
Presented By:
See Event on Google.Subscribe to Calendar
Seminar Description coming soon.
Evidence of Rift-Parallel Deformation Along the Western Branch and Main Ethiopian Rift?
Dec. 4, 2013
noon - 1 p.m.
Geology 1707
Presented By:
See Event on Google.Subscribe to Calendar
The East African Rift System spans N-S ~5000 km and currently experiences E-W extension. Previous kinematic studies of the EARS delineated 3 relatively rigid sub-plates (Victoria, Rovuma, and Lwandle) between the Nubian and Somalian plates. GPS observations of these block interiors confirm the rigid plate model, but new observations within individual rifts are beginning to show deformation that does not conform to large-scale E-W extension. Here we present (1) new velocity solutions based on GPS observations within the Main Ethiopian Rift, the southern Albertine Rift, and the Rungwe Volcanic Province, (2) a kinematic model for the Rwenzori block in the northern Western Branch and (3) preliminary work aimed at deciphering non-volcanic deformation within the Rungwe Volcanic Province such that we can detect the long-term tectonic deformation signal. Our velocity solutions suggest a possible systematic rift-parallel deformation pattern that has previously been undetected due to a lack of geodetic observations. We find that the existing kinematic models of the EAR are unable to explain the along-rift deformation, thus we developed a new kinematic model that includes the Rwenzori block within the Western Branch constrained by GPS observations and earthquake slip vectors derived from a local seismic network. Our early work suggests the Rwenzori block rotates clockwise relative to the Victoria block. Further south in the Rungwe Volcanic Province, we investigate a pre-2011 volcanic eruption velocity field to test the hypothesis of systematic along-rift deformation. Preliminary results indicate a possible inflation event prior to the 2011 volcanic eruption that must be removed from the pre-2011 volcanic eruption velocity field, from which we then observe rift-parallel deformation. Our work demonstrates the kinematics of individual rifts needs to be re-evaluated in the broader context of the East African Rift System.