Josh A. Calkins

Columbia University | CU · Lamont-Doherty Earth Observatory

We image the slab underneath a 450 km long transect of the Alaska subduction zone to investigate (1) the geometry and velocity structure of the downgoing plate and their relationship to slab seismicity and (2) the interplate coupled zone where the great 1964 earthquake (Mw 9.2) exhibited the largest amount of rupture. The joint teleseismic migratio...

Key Points Aleutian crustal structure determined through receiver functions Active source results constrain receiver function data using new method Parameters describing magma chamber estimated through forward modeling

The Pampean flat-slab region, located in central Argentina and Chile between 29� and 34�S, is considered a modern analog for Laramide flat-slab subduction within western North America. Regionally, flat-slab subduction is characterized by the Nazca slab descending to �100 km depth, flattening out for �300 km laterally before resuming a more “normal”...

Earthquakes in subduction zones are mostly generated at the interface between the subducting and overlying plates. In 2006-2009, the MOOS (Multidisciplinary Observations Of Subduction) seismic array was deployed around the Kenai Peninsula, Alaska, consisting of 34 broadband seismometers recording for 1-3 years. This region spans the eastern end of...

The Pampean flat slab region, located in Chile and western Argentina between 29° and 34° S, is characterized by the subducting Nazca plate assuming a sub-horizontal geometry for ~300 km laterally before resuming a more "normal" angle of subduction. The onset of flat slab subduction is associated with the cessation of regional arc related volcanism...

Rifting and ocean-basin forming events are active only in a few places, although they represent the best accessible evidence for the early stages of continental breakup. One such place is the Woodlark Rift, Papua New Guinea, where a transition occurs along strike (with distance to the Euler pole) from limited continental extension, to large extensi...

High-resolution 3-D shear velocity (Vs) images of the western Washington lithosphere reveal structural segmentation above and below the plate interface correlating with transient deformation patterns. Using a spectral technique, phase velocities are extracted from cross-correlated ambient noise recorded by the densely spaced ``CAFE'' broadband arra...

We present earthquake locations, scattered wavefield migration images, and phase velocity maps from preliminary analysis of combined seismic data from the Broadband Experiment Across the Alaska Range (BEAAR) and Multidisciplinary Observations of Onshore Subduction (MOOS) projects. Together, these PASSCAL broadband arrays sampled a 500+ km transect...

Receiver function analysis of seismic data from broadband stations along the Aleutian Arc provides new constraints on bulk velocity structure and thickness of the crust, and identifies intracrustal features, such as an upper crustal magma chamber and the top of the lower crust, in some portions of the arc. We collected data from January 2000- Decem...

The late Triassic to early Tertiary Coast Mountains Batholith (CMB) of British Columbia provides an ideal locale to study the processes whereby accreted terranes and subduction-related melts interact to form stable continental crust of intermediate to felsic composition and complementary ultramafic residuals. Seismic measurements, combined with cal...

The subduction interface beneath Western Washington hosts one of the first recognized and most reliably episodic zones of tremor and associated slow slip discovered at any subduction zone on earth, but produces very few thrust zone earthquakes. The thermal and petrologic conditions that contribute to this particular behavior along the Cascadia mega...

The Pacific-North America plate boundary, a young oblique rift system running lengthwise along the Gulf of California (GoC), is an excellent modern example of continental breakup and drifting. The central gulf (Guaymas transect) and the southern gulf (Alarcon transect) display robustly magmatic ocean crust production, but between these two transect...

One of the long-standing questions regarding mantle recycling is the role of sediment subduction on the silica enrichment of the continental lithosphere. Silica enrichment of the continetal lithosphere has been observed in a number of tectonic settings. Some of these settings are no longer associated with subduction, such as the Kaapvaal craton, wh...

Whether by accretion, magmatic addition, or refinement of more mafic lithologies, continental arcs are likely zones for the creation of "average" continental crust with intermediate silica content. This dissertation contains the results of broadband seismic studies carried out in two field areas, an active subduction zone and the remnants of an ext...

The Coast Mountains Batholith (CMB) of British Columbia provides an excellent locale to study the processes whereby accreted terranes and subduction-related melts combine to form stable continental crust of intermediate to felsic composition. Genetic and spatial relationships between adjacent geologic units, however, are largely obscured by widespr...

The main goal of the interdisciplinary Batholiths continental dynamics project is to understand how the composition, structure, and fabric of the crust and mantle evolved following the emplacement of the Coast Mountains Batholith (CMB). The major issue related to the CMB is determining whether crustal melting and distillation generated an ultramafi...

One of the overarching goals of the interdisciplinary Batholiths project is to investigate the structure and composition of the crust and upper mantle in search of evidence of a currently existing or previously delaminated ultramafic root beneath the Coast Mountains Batholith (CMB) in central western British Columbia. The southern transect of the p...

Flat slab subduction of the Nazca plate beneath the western margin of South America is thought to control the tectonic deformation of the Andean Precordillera and Sierras Pampeanas between 30° and 32° S. Several arrays of broadband seismic instruments have been deployed in Chile and Western Argentina to study this phenomenon (e.g., CHARGE, 2000-200...

Images of the crust and upper mantle obtained using teleseismic receiver functions exhibit a weak P-S conversion from the Moho in Western Argentina, where a segment of the subducting Nazca plate flattens out beneath the overriding South American plate. To better estimate depth to the Moho and search for mid-crustal impedance contrasts, we calculate...

The primary goal of the Continental Dynamics `Batholith' project is to constrain the petrogenesis of the Eocene Coast Mountain Batholith and determine the fate of the residual mass complementary to the massive Eocene granitic melt distillation event. The passive source component of this project was mobilized in June of 2005 and will be demobilized...

Images of the crust-mantle boundary and crustal structure obtained using the traditional analysis of teleseismic receiver functions (RFs) exhibit an unusually weak P-S conversion from the Moho in Western Argentina, where the subducting Nazca plate temporarily flattens out beneath the overriding South American plate. In order to better estimate dept...