If a fault moves at the bottom of the ocean, can anyone hear it?

A few hundred miles off the coast of Oregon, and under several miles of sea water, lies the Blanco Transform Fault. It is between the Juan de Fuca and the Gorda tectonic ridges. Ocean transform faults such as this one connect seafloor ridges and are where volcanic activity creates new oceanic crust. This fault is more seismically active than many faults on land, generating over 1,600 earthquakes in a single year (between 2012 and 2013). Did you feel anything then?

Location and tectonic setting of the Blanco Transform Fault.

Vaclav Kuna, a doctoral candidate in seismology in the College of Earth, Ocean and Atmospheric Sciences working with Dr. John Nabelek, is studying this fault—how it slips and how it moves, and whether its motion is seismic (involving an earthquake) or aseismic (slow movement without an earthquake). A collection of movements is called a seismic swarm. The hypothesis is that prior to large, seismic motions, there are small, aseismic motions. Through his research, Vaclav hopes to decipher what occurs in a swarm, and discover if there is a pattern in the fault’s motions.

The model Vaclav is working to develop of the mode of slip of the Blanco Transform Fault. We believe that slow (non-seismic) creep occurs at depth in the fault beneath the Moho and loads the shallower part of the fault. The slip at depth most likely triggers the big earthquakes, that are preceded by foreshocks associated with creep.

This is different than predicting earthquakes. As a seismologist, Vaclav is trying to understand and report on the behavior of a fault, not predict when a certain magnitude earthquake will occur. However, other researchers can use findings like Vaclav’s to create prediction models which are necessary for earthquake damage mitigation and increasing public safety during and after earthquake events.

To look for patterns in the fault’s motions, Vaclav analyzes a year’s worth of data from seismometers and pressure gauges that were deployed from a ship to the fault at the ocean floor several years ago. The seismometers measure the velocity of a fault’s movement in three directions (two horizontal and one vertical), and the pressure gauges act as microphones capturing sound waves. The data can be decomposed into a series of many waves (like sine or cosine waves). Vaclav can track these waves in the sensors deployed along this fault and determine the variability of motion in both time and space. After the sensors are finished collecting the data, a remote control turns on an electrical circuit, that triggers a corrosion reaction and severs a wire holding a large weight that is keeping the sensors at the ocean floor—which seems like something taken right out of a spy movie.

Deployment of ocean bottom seimometers (yellow packets) at the Blanco Transform Fault. Every packet includes a 3-component seismometer and a differential pressure gauge (which acts as a microphone).

So why would a researcher monitor a fault that is miles underwater when there are faults on land? Ocean transform faults are less complex than faults on land, making them desirable to study in order to answer fundamental questions about fault behavior. In addition, they are extremely seismically active and generate earthquakes more frequently than faults on land. However, ocean transform faults are evidently more difficult to observe, and because the process of planning for and conducting fieldwork is time-intensive, most of the data Vaclav uses were gathered before he was enrolled at OSU. In turn, Vaclav helps deploy sensors and gather data for future students to analyze at a number of different faults around the world.

Vaclav at a station deployment at the Kazbegi mountain, Georgia (Caucasus mountain range).

Vaclav did his Bachelor’s and Master’s degrees in Geophysics in Prague, Czech Republic. He was motivated to study Geophysics because there is a lot that is unknown about how the Earth’s tectonic plates move, and many people living near these faults. In his spare time, Vaclav likes swimming, running, skiing and kayaking. After completing his PhD, Vaclav wants to find a job working towards hazard-related mitigation to help people who are vulnerable to the damages caused by earthquake hazards.

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