iPlex Lunch - fall-2016

Oct. 5, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

• Lingling Ye - Caltech

Seminar Description coming soon.

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

Presented By:

• Jacqui Gilchrist - SCEC-USC

Seminar Description coming soon.

Oct. 19, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

• Heather Ford - UCR

Lowermost mantle flow along the edge of the African superplume: What can shear wave splitting analysis tell us?

Oct. 26, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

• Robert Martin-Short - UCB

Seminar Description coming soon.

Nov. 2, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

• Mortaza Pirouz - Caltech

Flexural bending of the Zagros Foreland basin

Flexural deflection of the Arabian plate is modeled using point load distribution and convolution technique. The results are compared to the constrained flexural depression of the Zagros foreland obtained from subsurface data from Iran, Iraq and Syria for the entire northern edge of the Arabian plate. The Oligo-Miocene Asmari Formation, and its equivalents in Iraq and Syria are used to estimate Arabia-Eurasia post-collisional subsidence. This extensive rigid carbonate platform limestone separates passive margin sediments from the younger foreland deposits. In order to obtain geometry of the Asmari limestone in the Zagros foreland, we compiled a large database of well logs, seismic profiles and structural sections to track Asmari depth beneath the Mesopotamian basin and the Persian Gulf. Our results show that the foreland depth is not constant along strike of the Zagros wedge and varies between 1 and 6 km. The deepest part of the foreland is located beneath the Dezful embayment in Iran and becomes shallower towards both ends. The resulting geometry is clearly consistent with the interpretation of the basin as a simple flexural foreland loaded by the Zagros orogenic wedge. In this study, we investigate how the geometry of the foreland relates to loading by the range topography focusing on the eastern sector. We then show the observed geometry and gravity data over the foreland and range topography can be well reproduced with a simple flexural model which only assumes loading due to sediments, topography and crustal thickening. The equivalent elastic thickness of the flexed Arabian lithosphere is estimated to be 52km, and decreases beneath the range. We find no evidence for any other main source of loading of the lithosphere, either related to the density variations or dynamic origin. The model also implies about 120 km of mean crustal shortening across the entire Zagros, which represents shortening in both the basement as well as the sedimentary cover. Furthermore, predicted Free-Air anomaly using our Moho depth model shows much better agreement with the observed Free-Air anomaly than the Free-Air anomaly derived from other published seismic Moho depths.

Nov. 9, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

• Edward Rhodes - UK, New Zealand slip rates

Slip rates on the Wairau, Awatere, Clarence, and Hope faults, South Island, New Zealand

Nov. 16, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

• Mong-Han Huang - JPL

Coseismic fault slip and triggered landslides of the 2016 Mw 6.2 Amatrice earthquake in Italy

Central Italy has had multiple moderate size but damaging shallow earthquakes. In this study, we optimize the fault geometry and invert for fault slip based on coseismic GPS and Interferometric Synthetic Aperture Radar (InSAR) for the 2016 Mw 6.2 Amatrice earthquake in Italy. Our results show nearly all the fault slip occurred between 3 and 6 km depth but extends 20 km along strike. There was less than 4 cm static surface displacement at the town Amatrice where the most devastating damage occurred. Landslides triggered by earthquake ground shaking are not uncommon, but triggered landslides with sub-meter movement are challenging to be observed in the field. We find evidence of coseismically triggered landslides northwest and northeast of the epicenter where coseismic peak ground acceleration was estimated > 0.5 g. By combining ascending and descending InSAR data, we are able to estimate the maximum landslide thickness as at least 100 and 130 m near Mt. Vettore and west of Castelluccio, respectively. The landslide near Mt. Vettore terminates on the pre-existing fault Mt. Vettore Fault (MVEF) scarp. Our results imply that the long-term fault slip rate of MVEF estimated based on paleoseismic studies could potentially have errors due to triggered landslides from nearby earthquake events.

Nov. 23, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

• Adriano Gualandi - Caltech

Geodetic time series data are usually studied through classical statistical techniques, that is decomposing them into different deterministic signals. Recently, multivariate statistical techniques have been applied to geodetic data, in order to extract as much information as possible from them. An example is the Principal Component Analysis (PCA), used both to detect network errors in GNSS data and to identify geophysical signals common to a certain region. The latter approach is particularly useful for understanding geophysical processes. Nonetheless, a strong limitation of the PCA is that it is not able to separate multiple mixed sources. In other words, the PCA technique is not effective in treating the so-called Blind Source Separation (BSS) problem. For this goal, it reveals to be an efficient technique the Independent Component Analysis (ICA). I will introduce an ICA technique based on the Variational Bayesian approach, and the results concerning both tests on synthetic data and application to real data. In particular, I will show results from the study of the Gorkha 2015 earthquake (Nepal), the Slow Slip Events in Guerrero (Mexico), and the deformation in the region of the Altotiberina fault, a low-angle normal fault in the northern Apennines (Italy).

Nov. 30, 2016
noon - 12:50 p.m.
Geology 1707

Presented By:

• Simran Sangha - UCLA

Source solution of the 2015 Mw 7.2 Murghab, Tajikistan earthquake from InSAR and seismological data

Combining space-based geodetic and array seismology observations can provide detailed informations about earthquake ruptures in remote regions. Here we use Landsat-8 imagery and ALOS-2 and Sentinel-1 radar interferometry data combined with data from the European Seismology Network (EU) to describe the source of the December 7, 2015, Mw7.2 Mughrab (Tajikistan) earthquake. The earthquake reactivated a 70 km-long section of the Serez-Karakul fault, a NE oriented sinistral, trans-tensional fault in northern Pamir. Pixel offset data delineate the geometry of the surface break and line of sight ground shifts from two descending and three ascending interferograms constrained the fault dip and slip solution. Two right-stepping, NE-striking segments connected by a more easterly oriented segment, sub-vertical or steeply dipping to the west were involved. The solution shows two main patches of slip with up to 3.5 m of left lateral slip on the southern and central fault segments. The northern segment has a left-lateral and normal oblique slip of up to a meter. Back protection of the high frequency (0.5-2.0 s) band of seismic data recorded by the EU network processed using the Multitaper-MUSIC approach focus sharply along the modeled fault. The time progression of the high frequency radiators shows that, after a 10 seconds initiation phase at slow speed, the rupture progressed in 2 phases at super-shear velocity (~6 km/s) separated by a ~10 seconds interval of slower propagation corresponding to the passage through the restraining bend. The intensity of the high frequency radiation reaches maxima during the early and middle phases of slow propagation and is reduced by ~50% during the super-shear phases of the propagation. These findings are consistent with other studies on other strike-slip faults in continental domain, showing the importance of the fault geometric complexities in controlling the speed of fault propagation and related high frequency radiation pattern.