Improving and developing seismic imaging techniques

The crux of my research relies on creating high-resolution images of crustal and uppermost mantle structure; a challenging area considering the largest variations in seismic characteristics occur at these depths. Improving and modifying seismic imaging techniques is necessary to advance our understanding of how tectonic events are manifest in the seismic characteristics of a region. In my research, I have developed new approaches for the creation of 3D shear-wave velocity models that improve the lateral resolution of geologic structures at depth through the joint inversion of surface wave dispersion and adaptively binned receiver function data (Delph et al. 2015b, 2017a, 2017b). I am also interested in applying interferometry techniques to both earthquake and ambient noise data to understand the body-wave discontinuity structure of the crust and upper mantle (e.g., Delph et al., 2019; GitHub code).

The effects of fluid on subduction zone processes

Petrologic, mechanical, geophysical, and modeling constraints indicate that the dewatering of oceanic lithosphere during prograde metamorphism in subduction zones is responsible for intermediate-depth seismicity and non-volcanic tremor. I am interested in investigating when, where, and how the oceanic lithosphere is hydrated, and how dewatering affects the seismic characteristics of the overriding plate and subduction interface. My work in Cascadia has shown that lateral variations in seismicity, tremor, gravity anomalies, volcanism, and seismic velocity in the overriding plate are related to the depth and distribution of fluid release from the downgoing plate along the subduction margin.

Relevant Publications: Delph et al. 2018; Condit et al. 2020; Koch et al. 2020; Delph et al. 2021a

The termination of subduction

Anatolia (modern day Turkey) is located at the transition between the continuous subduction of oceanic lithosphere in the west (beneath the Aegean) to complete ocean basin closure and continent-continent collision in the east (Arabia-Eurasia collision), with a contorted and deforming slab separating the two end-members in central Anatolia. Thus, this margin provides a spatial analogue to the temporal evolution of a subducting plate as continental lithosphere approaches the trench. By understanding along-strike variations in the overriding plate, and connecting them to the behavior of the downgoing plate, we may be able to gain insight into the processes that accompany the terminal stages of subduction.

Relevant publications: Delph et al. 2015a, 2015b, 2017b; Reid et al. 2017; Abgarmi et al. 2017; Portner et al. 2018; Reid et al. 2019; Cosca et al. 2021; Lynner et al. 2022; Kaviani et al. 2022

Lithospheric-scale magma plumbing systems and the creation of silicic crust

Melt from the mantle is primarily basaltic, while continental crust is dominantly intermediate in composition. As continental crust comprises 70% of the volume of total crust on the Earth, the question of how we create large volumes of silicic material is an ongoing area of research. The Altiplano-Puna Plateau of the Central Andes in South America provides an opportunity to investigate the volumes and extent of magmatism a long-lived subduction system is capable of producing. This region has a long history of crustal shortening, growth, compositional differentiation, and lithospheric delamination, and recent seismic images of large silicic magmatic bodies beneath extensive silicic ignimbrite fields indicate that these Cordilleran-type systems are capable of generating a large amount of silicic crust over relatively short amounts of geologic time.

Relevant Publications: Delph et al. 2017a; Ward et al. 2017; Koch et al. 2021; Delph et al. 2021b

The resiliency of cratonic crust

By integrating the geologic history of cratonic regions with the observed seismic characteristics of the crust, we can better understand whether the observed characteristics are useful for discussions of secular variation in crustal formation processes, or alternatively, how different tectonic events modify architecture of the crust. Southern Africa comprises some of the oldest rocks on the planet, as well as some of the oldest recorded orogens. We find a good correlation between tectonic events that occurred “post” cratonization and the character of the crust, indicating that the inferred resiliency of cratonic lithosphere may not extend to the crust. This indicates that seismic observations of crustal structure in cratonic regions must be carefully examined with respect to the tectonic events that have affected the region in order to make arguments about the characteristics of initial crustal formation in cratons.

Relevant Publications: Delph et al. 2015c