Category: PALNews (page 1 of 8)

News related to the PAL

AVF P-wave travel time tomography: 100+ teleseismic events

We implement P-wave travel time tomography using FMTOMO, to image the subsurface structure beneath the Auckland Volcanic Field. The input information, which is the residual travel time is obtained using an adaptive stacking code, tcas by Nick Rawlinson. Inversion is then implemented using more than one hundred teleseismic sources.

getting the residual time: tcas

The code tcas works by taking the predicted time (eg. using ak135 1-D Earth model) to a reference station to be compared with other stations. The difference between the predicted time is the base for the approximate initial alignment. Cross correlation is then performed to create the final improved alignment from which we get the residual time from the 1D-Earth model that we used.



teleseismic inversion

We apply to the tcas code 131 earthquakes limited to epicentral distance greater than 27 degrees to avoid triplication of the P-wave arrival.


100+ events


The output residuals at every stations are plotted on a map to gauge the underlying trend in velocity field. Red color on the map shows positive residual which means larger than average value thus a slow field and vice versa for blue. The size of the circle shows how big is the residual. The indication is that there is a prevalent slow region to the east of the AVF.



Inversion improve the preliminary trend by showing with more precision the split from positive to negative anomaly. The split is striking Northwest-Southeast extending to 80 km deep. We interpret this to be related to the Junction Magnetic anomaly of the Dun Mountain Ophiolite Belt.


Teleseismic inversion


Zoe is off to Bristol to join the PhD programme

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!

Combined ultrasonic and photoacoustic imaging of the carotid artery

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!

Jupyter notebooks for mathematical methods in the physical sciences

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 wrote 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. We are going to assume you run python 3.

You can get the entire repository of notebooks from our github site, or get one at a time by clicking on a chapter hyperlink below:

  1. Introduction
  2. Dimensional analysis, with an example of Buckingham Pi Theorem to flying objects.
  3. Power series, and the trajectory of a bouncy ball
  4. Spherical and cylindrical coordinates applied to the Gaussian function and its integral
  5. Gradient applied to topographic data from Auckland
  6. Divergence, and the flow of fluids and vortices
  7. Curl, rigid rotation, and curl-free fluid flow
  8. Theorem of Gauss, with gravity from the atmosphere to the centre of the Earth
  9. Theorem of Stokes and the Biot-Savart Law
  10. The Laplacian,  and the shape of a soapy film

PORO/PAL party during the GSNZ meeting

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 got engaged!

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).

Apple Seismology

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.

Resolution test on the AVF

We propose to perform P-wave tomography to infer the structure beneath the AVF, with Nick Rawlinson’s FMTOMO. Our first step is to establish the resolution that we can expect from this exercise. Below, we plot the locations of the earthquakes — a total of 1330 cataloged events, 681 local + 649 teleseismic — used in this test:



The local events made up the sources coming in from the southeast of the receivers array. Whereas teleseismic sources complement this with incoming rays from other directions but most notably from the Northwest.

We compute synthetic seismic P-wave arrival times for the AVF seismic stations, as if the earth structure under the AVF has a checker-board pattern. For this test, this will be our “true” model of the Earth. And so the objective of this test is to invert these synthetic travel times to recover the “true” model checker-board pattern. Regions where the inverted results show a checker-board pattern suggest a good resolution. And the size of each checker-board pattern imply the size of the smallest feature resolvable.

Coarse Checker-board Test

The first checker-board model shall have a wide grid spacing creating a fairly large checker-board patterns. In the following image, the ensuing checker-board model is represented by the three panels on the left while its recovery after the inversion is represented by the panels on the right.


Large checker-board test



  • Dimension of the region where resolution is most exemplary is signified by the red box, ranging from Northland to Waikato, and to 280 km depth.
  • Outside of the box, the smearing artefact is too prominent. Caused by ray paths having similar orientation.
  • Within the box, the size of the features that are resolvable, corresponds to the size of each checker-board, is in the order of 60 km.

Fine Checker-board Test

We reduce the grid spacing, creating a smaller sized checker-board model, inferring that smaller features now have the potential to be resolved.



  • The red box where resolution is commendable, is now span over the Auckland region, down to about 80 km deep.
  • Within this box, subsurface features on the scale of 30 km can be resolved.

Congratulations, Dr. Jami Johnson!

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.


Postgraduate opportunities in our lab

Below are short descriptions of research projects available for postgraduate students in our group at the University of Auckland. If you are interested in any of these, please contact us for technical questions. For questions around enrollment at the University of Auckland, please go here. Scholarships may be available for the best applications through the University of Auckland, or the Dodd Walls Centre.

ResonanT Ultrasound Spectroscopy

Resonant ultrasonic spectroscopy fills an important gap between our ultrasonic and seismic research. Together with the PORO lab, we have rock samples to complement laser ultrasound and a host of other petrophysical data with new RUS results.

Laser ultrasonic rock physics under high pressure and/or temperature

The PAL and PORO lab join forces by combining our respective strengths in laser ultrasound and rock physics to improve data quality and quantity. In this project, we are building the expertise to do laser ultrasound in a pressure vessel with optical windows. Source/receiver locations are varied under computer control with an arduino-controlled servo rotational stage.

unraveling the mysteries of the Auckland volcanic field

Part of an active volcanic field, questions surround the nature of Auckland’s past, present and future. Using a suite of seismic techniques that range from ambient seismic noise tomography, to receiver functions and body wave tomography, we aim to build a representative model that helps us explain the geodynamics of the Auckland Volcanic Field.

quality control of timber and fruit products with laser ultrasound

Laser ultrasound can be applied to products of interest to a wide community. Current methods of testing the quality of fruit and timber, for example, can often be described by one or more of the following terms: sparse, contacting, expensive, and often destructive. In this project, we aim to explore the opportunities for laser ultrasound in estimating the quality of  fruit and timber in a non-contacting and non-destructive matter.

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