Physical Acoustics Lab

Last week, was graduation at the University of Auckland. Two PALS received degrees from the faculty of science: Jonathan Simpson received a BSc (honours) in Geophysics, and Rabea Pleiss graduated as a Science Scholar with a BSc in Geophysics, as well. We are very proud of them, and are pleased that both will be with us a bit longer for MSc degrees. In Rabea’s case, this won’t be for a few months, as she’s off to Central America first!

The Auckland Volcanic Field (AVF) contains surface expressions of more than 50 volcanic eruptions (red in the figure below). The last eruption, Rangitoto Island, was only 600 years ago! Why the AVF is here, remains a question to this day. The field is not on a plate boundary, but also not a intraplate volcanic field such as the hotspots of Yellowstone and Hawaii.  GeoNet has instrumented the area with a network of seismometers (black circles). Seismologists monitor the AVF with this network, while the DEVORA project studies the geologic hazard and risk associated with the AVF.

Seismic activity in the area is actually relatively low, but recent advances in seismology allow us to study the subsurface using seismic surface- and body waves.

Surface Waves

Noise of the city and the surrounding oceans generate seismic surface wave energy. We extract information between seismic stations as if one of the seismic stations were the source (the “earthquake”) and the other the recorder. To do this properly for all stations in the AVF, we first need to determine the orientation of each seismic station.

Body Waves

Earthquakes from regional and teleseismic events provide P- and S-waves for body tomography. A synthetic checker-board test helped us determine the expected resolution, after which we embarked on a preliminary  tomographic inversion using data from 100+ teleseismic (far away) events.

Zoe, one of the original Apple Seismologists, is off to the University of Bristol, UK! She’s going to be working with Dr Judy Rorison in the Photonics team. She works primarily in development of fundamental materials for use in Optoelectronics focusing on the use of Quantum Photonics/ Quantum Dots and Wells, and development of Optoelectronic devices. After obtaining her Btech degree in the PAL, Zoe worked for Vodafone, but is now ready to accept a new challenge in the UK. All the best, Zoe, and please stay in touch!

Today, Dr. Jami Johnson’s final PhD thesis chapter found its way into the peer-reviewed literature. Her work on combined laser ultrasound and photoacoustic imaging of an ex-vivo carotid artery has appeared in the March issue of Photoacoustics. The PALs involved (Jami and Kasper) would like to thank our external collaborators: Merv Merrilees and Jeff Shragge for this exciting and ultimately very successful experience!

A Guided Tour of Mathematical Methods for the Physical Sciences is based on a philosophy that learning mathematics for the physical sciences, requires pen and paper. Learning by doing. Three editions in, this philosophy still holds strong, but heaps of things have happened since the first edition in 2001. Numerical methods play an ever-larger role in the physical sciences, for example. The Python programming language has really exploded on the scene, and more recently the jupyter notebook has been developed to facilitate learning numerical methods in python. To accompany the latest edition of our book – and your pen and paper – we are writing one jupyter notebook per chapter.

If you are new to jupyter notebooks and/or python, the online resources are virtually endless, and the installation — on any operating system — is easy with conda. You can download, and even run, the notebooks here.

From left to right: Steve Brennan, Sam Hitchman, Paul Freeman, Kasper van Wijk, Evert Duran, Josiah Ensing and Jonathan Simpson.

This week the annual GSNZ meeting  was on University of Auckland campus. To celebrate a successful year in research, we hosted a small get together in our labs for tours, demos, drinks and some food. Below are a few photos as proof, despite the “zapruder film” quality of these…

Sam showing Professor Martha Savage and other guests his new optical rock strain (and temperature) meter

James Clarke giving an overview of the research projects and equipment in the PORO lab to a captivated audience.

Evert Duran with guests, including Professors John Townend and David Prior.

Shreya Jagdish Kanakiya and Josiah Ensing

Jami Johnson sent us word of her engagement to her Kiwi  boyfriend Sam! Here is a picture of the happy couple on a recent trip to Norway. We wish Sam and Jami all the best (and for them to move back to New Zealand, of course).

Today, our paper on Apple Seismology appeared in Physics Today. It was a follow up on Sam and Zoe’s experiments, highlighting the similarities between seismic waves and normal modes in the Earth, and their acoustic equivalents in a Braeburn apple.

In the panel on the left, seismic (surface) waves traverse Earth, while in the right panel laser-generated and detected surface waves circle the apple.

It’s the end of an era… Jami Johnson successfully completed her PhD thesis in photoacoustic imaging.  She is now off to The University Pierre and Marie Curie, in Paris (France) to pursue postdoctoral research in medical imaging. We wish Jami all the best, and we will follow her in what will undoubtedly be a very exciting career. The PALs want to thank Jami for all her efforts and the wonderful memories she leaves behind.