Karin Sigloch

(Seismology)

Department of Earth and Environmental Sciences
Geophysics
Munich University
Theresienstr. 41
80333 Munich
Germany

Room: 442
Phone: +49 (89) 2180-4138
Fax: +49 (89) 2180-4205

Research

My primary research interest is in seismic tomography, the science and art of making three-dimensional maps of the Earth's deep interior, from crust to core - essentially mapping temperature variations. Thermally driven motions shape the face of our planet and ultimately enable life on Earth. Understanding this "convection machine" is therefore of fundamental interest, and seismic imaging is the most immediate leverage point on the problem.

Mantle structure beneath western North America, as obtained from seismic tomography. This is a bird's-eye view from south-east. The rainbow-colored 3-D contours outline the Farallon plate, from the surface down to 1800 km depth. The tectonic plate once formed the sea floor of what is now the Pacific Ocean basin, but it has been gradually been sinking back into the mantle over the past 200 million years. In the process, it has thrust up the spectacular mountains that characterize this region today (surface topography is overlain in translucent blue/green/brown shades). This ancient plate is still detectable because seismic waves travel slightly faster through it than through the ambient mantle.

From a global-scale perspective, we cannot physically sample the earth's interior to significant depths in situ (the deepest hole drilled is less than 20 km, but earth's radius is 6371 km). Instead we use naturally occurring strong earthquakes as probes. Their radiated seismic energy travels through the entire globe, and is recorded by seismometers deployed across the world's surface. From slight distortions in the recorded waveforms, and thousands or millions of crossing wavepaths, we infer temperature and density anomalies throughout the volume of the earth. This amounts to remote surveying of the earth's interior, and is conceptually equivalent to the non-invasive, 3D imaging methods used for medical diagnostics. Progress in the field of seismic tomography is largely driven by the growth of supercomputing capabilities (and prospective graduate students should be motivated to use these tools).


I pursue two main lines of research:

(1) The push for better methodology in the imaging techniques that should result in much sharper, more detailed pictures. Collectively, such methods are referred to as "waveform inversion", and have in common their extensive use of high-performance computing infrastructure. I mainly pursue a variant called "finite-frequency tomography", which is particularly suited to imaging on continental and global scales. More recently, I have also become involved in so-called "global search" (Bayesian, Monte Carlo) methods, which can fully assess the uncertainties and "blurriness" of the obtained images. Together with colleagues from applied geophysics, we are developing tomography methods for very small sample scales (centimeters in the case of ultrasonic waves, tens of meters in the case of shallow seismics.)

(2) Understanding tomographic pictures in terms of earth processes and earth history. This big-picture challenge requires making qualitative and quantitative links to the neighboring disciplines: geology, geodynamics, plate reconstructions, mineral physics, and geochemistry.
Many structures that we observe in the interior (subducted plates) were located at the surface in the distant geological past, and left their traces on ancient land forms and life, which are independently observed by geologists today. Hence tomography provides a complementary window into the past ~200 million years. Of course the interpretation of tomographic images must be consistent with current surface activity, and they may even give glimpses of the distant future (e.g., sites of future volcanism).

On seismic time scales (seconds), the earth behaves mostly like an elastic body. This explains seismology's big success as an observational, data-rich discipline. On geological time scales (millions of years), the mantle behaves like a viscously advecting Navier-Stokes fluid, driven by internal heat that was trapped when the earth formed. But the mantle behaves unlike any rheology observed at surface conditions and time scales. Understanding of mantle flow must thus be gained indirectly, combining the instantaneous snapshots provided by seismic tomography with plate tectonic reconstructions of the past, and with geodynamical computer simulations.

Below are short descriptions of some current and past research projects. Prospective graduate students are encouraged to inquire directly, since not every open position is posted online immediately.