Helen Janiszewski

PhD Candidate | Columbia University

Welcome! I'm a fifth year PhD student at Columbia University. I use seismic waves to learn about the interior structure of the earth, particularly at subduction zones. Take a look around to find out what I'm working on in my research and what else I'm up to. Or download a copy of my CV for the executive summary.

Research

My research is focused on using a variety of types of seismic data to better understand the structure of the crust and upper mantle in subduction zone environments. For my dissertation I am using receiver functions, surface wave dispersion, and wide-angle reflection data to better understand the along-dip and along-strike thermal and structural variability of the Cascadia subduction zone. I am taking advantage of data from the Cascadia Initiative Community Experiment, which has provided an unprecedented ocean bottom seismometer (OBS) array that covers the entire Juan de Fuca plate. This allows a complete seismic image of the plate from its creation at the ridge, across an aging plate to the trench where subduction begins, through the locked portion of the megathrust, and continuing onshore past the volcanic arc. This has also been my first foray into using OBS data and I have become very interested in the effectiveness of noise removal techniques and general data quality in relation to site and instrument properties.


Surface Wave Imaging of the Juan de Fuca Plate

Surface waves from teleseismic earthquakes can help us constrain seismic shear wave velocities related to lithospheric structure. Using the ASWMS package we create phase velocity maps that cross the coastline, extending over the entire Juan de Fuca plate and Cascadia subduction region (shown adjacent, using Cascadia Initiative data years 1-3). We see evidence of features such as the subducting slab, the transition from oceanic to continental lithosphere, the Juan de Fuca ridge, and the volcanic arc. The incorporation of the final year of data and using tilt and compliance corrections on the OBS instruments will improve our data quality and coverage.

Imaging the Plate Interface in the Cascadia Seismogenic Zone

The Cascadia subduction zone has historically produced up to M 9 megathrust earthquakes; however, there is much uncetainty about the structure of the plate interface within the locked zone and its relationship to the structure of the subducting crust down dip. We use receiver functions (example of data shown adjacent; Janiszewski and Abers, 2015) from OBS stations deployed on the continental shelf off the coast of Washington to extend onshore receiver function studies offshore. We found that models that contained a low velocity zone along the plate interface were consistent with the data, which may indicate that a weaker boundary persists into the locked zone. This study is also complemented by a ship-to-shore wide angle reflection dataset in the same area, that will provide constraints on the variability of reflectivity associated with the subducting Juan de Fuca crust across the coastline.

Variability of Noise and Effects of Corrections at the Cascadia OBS Instruments

Any seismologist knows there are significant gaps in our instrumentation in the oceans. The Cascadia Initiative filled some of these gaps with a plate scale OBS deployment over four years in water depths from ~ 4500 - 55 m using multiple instrument types, including newly designed shielded instruments. In the process of using both receiver functions and teleseismic surface waves, we've noticed significant variability in data quality, both across sites in the array and between the two data types. This has led to an exploration of the relationships between noise, site, and instrument properties as well as the effects of tilt and compliance corrections on these data sets. Shown adjacent is a comparison of an original and compliance corrected vertical record (10-100 s) from a teleseismic event recorded at two OBS sites in different water depths; the magnitude of correction is significantly larger for the shallow water site. Understanding these differences will help develop a more streamlined processing workflow adaptable for specific data types.

Crustal Structure along the Aleutian Island Arc

The Aleutian island arc is an ideal setting for studying the role of island arcs in continental crust production due to its relative stability and lack of pre-existing volcanism. We used receiver functions to estimate the crustal thickness and average Vp/Vs beneath each of the 13 permanent seismic stations deployed along the Aleutian island arc (shown adjacent, Janiszewski et al., 2013). These results are compared to the average thickness and composition of continental crust to better understand the process by which island arcs may build continents. We were also able to see evidence of a magma body beneath Akutan volcano due to back azimuthal variation in receiver functions. This work was part of the Lamont Summer Intern Program.

Publications


Papers

  1. Janiszewski, H. A., G. A. Abers, (2015) Imaging the plate interface in the Cascadia seismogenic zone: New constraints from offshore receiver functions, Seismological Research Letters, v. 86 no. 5 p. 1261-1269, doi: 10.1785/0220150104. (PDF)
  2. Janiszewski, H. A., G. A. Abers, Shillington, D.J., and J. A. Calkins, (2013) Crustal structure along the Aleutian island arc: New insights from receiver functions constrained by active source data, Geochem. Geophys. Geosys., 14, 2977-2992, doi: 10.1002/ggge.20211. (PDF)

Recent Conference Abstracts (First Author Only)

  1. Janiszewski, H. A., J. B. Gaherty, G. A. Abers, Surface-Wave Imaging of the Juan de Fuca Plate and Cascadia Subduction Zone, Abstract T44B-03 presented at the 2015 Fall Meeting, AGU, San Francisco, Calif., 14-18 Dec. (Talk). Received Honorable Mention for the Geoprisms Student Prize
  2. Janiszewski, H. A., J. B. Gaherty, G. A. Abers, Imaging the Cascadia subduction zone with surface waves, 2015 OBS Symposium, Vancouver, WA
  3. Janiszewski, H. A., G. A. Abers, H. D. Carton, J. B. Gaherty, Imaging the Locked Zone of the Cascadia Subduction Zone Using Receiver Functions from the Cascadia Initiative, Abstract T41E-07 presented at the 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 Dec. (Talk)
  4. Janiszewski, H. A., G. A. Abers, J. B. Gaherty, H. D. Carton, Imaging the downgoing Juan de Fuca crust using receiver functions from the Cascadia Initiative, 2014 Amphibious Array Facility Workshop, Snowbird, UT. (Talk)
  5. Janiszewski, H. A., G. A. Abers, H. D. Carton, S. C. Webb, J. B. Gaherty, A. M. Trehu, Imaging the Cascadia Thrust Zone using Active and Passive-Source Seismic Data, 2014 IRIS Workshop, Sunriver, OR.
  6. Janiszewski, H. A., G. A. Abers, H. D. Carton, S. C. Webb, J. B. Gaherty, A. M. Trehu, Active and passive-source imaging of the Cascadia subduction zone using both onshore and offshore data, Abstract S12A-03 presented at the 2013 Fall Meeting, AGU, San Francisco, Calif., 9-13 Dec. (Talk)

Other Involvement

Below is a list of other groups, projects, and organizations I have been involved with.


Seismology Student Workshop

Held annually in March at the Lamont Doherty Earth Observatory for the past four years, this is a research workshop organized by students exclusively for students broadly focused on seismology and related fields. It gives students the opportunity to present their research, learn about new topics, and network with other students in a low pressure environment compared to a traditional conference. Since its inception, the workshop has grown from a regional northeastern event to an international conference with over 50 attendees. I have been a part of the organizing committee for the past two years. More information.


Graduate Student Advisory Council

The Graduate Student Advisory Council at Columbia University is the main student government for all PhD students at Columbia University, as well as arts and sciences MA students. It is a source of advocacy, funding, and events for graduate students. I was elected to the steering committee for three terms, once as Communications Chair (2013-2014) and twice as Vice President of Administation (2014-2016). More information.


Field Projects

Contact Me

Email: helenj(at)ldeo(dot)columbia(dot)edu
Office: 201B Seismology, LDEO, Palisades, NY
Research Gate
Google Scholar
Twitter: @helenjanisz (mostly seismology related retweets)
Flickr: janiszphotos (a somewhat curated selection of my photos)