Chastity Aiken




Ph.D. Candidate, Seismologist

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Current Research:
Research Interests (new):


Earthquake-Earthquake Interactions
Surface waves of large, distant earthquakes can trigger earthquakes in the near-field (<100 km) and far-field (>100 km) in differing tectonic regimes, including extensional, transtensional, and transpressional environments. Geothermal/volcanic regions are mostly associated with extensional or transtensional environments and are often seismically active due to on-going geothermal productivity (energy resource) and active magmatic processes.

Earthquakes generate stress changes in Earth's curst due to permanent deformation (static) and passing seismic waves (dynamic). Both static and dynamic stresses can load faults and push them closer to failure. In the near-field, static stress changes are capable of promoting failure on adjacent faults, resulting in increased seismic activity such as earthquakes. On the other hand, dynamic stresses from passing seismic waves are capable of triggering earthquakes well beyond the aftershock zone where static stress changes no longer dominate.

As part of my dissertation, I investigated dynamically triggered earthquakes in active geothermal/volcanic regions, and this work has been published in Journal of Geophysical Research: Solid Earth. In Aiken and Peng [2014], we investigated similarities and differences in earthquake triggering among three geothermal/volcanic regions of California: Long Valley Caldera, Coso Geothermal Field, and Geysers Geothermal Field.
Please feel free to contact me about future research projects regarding this topic. (Send me a message.)


Example of earthquake triggering in Geysers by the 23 June 2001 M8.4 Peru earthquake.



Earthquake activity around time of Peru earthquake.



Earthquakes on seismogram envelope function around time of Peru earthquake.




Earthquakes triggered by Peru earthquake surface waves, as seen on a spectrogram.



Surface waves of Peru earthquake.



Seismogram showing earthquakes triggered by Peru earthquake surface waves.


Triggered earthquakes have distinct P and S waves on the seismogram.


Earthquake-Tremor Interactions
Surface waves of large, distant earthquakes can also trigger tremor in the near-field (<100 km) and far-field (>100 km), but this phenomena has only been observed in compressional and transpressional environments, such as in subduction zones and along strike-slip faults. Within strike-slip faults, tremor occurs at 25-35 km depths, beneath the seismogenic zone where earthquakes occur. Because of tremor's proximity to earthquakes, it is possible that tremor plays a role in earthquake occurrence. Thus, it is important to understand where tremor occurs.

Part of my dissertation has focused on identifying strike-slip fault regions where tremor has not previously been observed. One way to find tremor is to search for triggered tremor. Searching for triggered tremor is easier because (1) we know that the potential for triggered tremor is greatest during the large amplitude surface waves of distant earthquakes and (2) triggered tremor has a higher signal-to-noise ratio than tremor that occurs spontaneously. From my search of triggered tremor on strike-slip faults, I have identified tremor along the Queen Charlotte Margin [Aiken et al., 2013], the Eastern Denali Fault [Aiken et al.,2014, revised], and other strike-slip faults in the Western Hemisphere [in prep].
Please feel free to contact me about future research projects regarding this topic. (Send me a message.)


Examples of tremor triggered along four strike-slip faults in the Western Hemisphere
Each small panel shows the surface waves of an earthquake (bottom) and of triggered tremor (top). The year and name of the earthquake that triggered the tremor is above each panel. Gray triangles mark where the seismogram was recorded. Gray lines mark plate boundaries.



Ambient Tremor Activity

There are two types of tremor - tectonic and volcanic tremor. Tectonic tremor is observed along faults while volcanic tremor is observed around volcanoes. Both are equally important for understanding deformation processes in Earth's crust.

Tectonic tremor occurs at depths of ~25-35 km (on strike-slip faults), beneath the seismogenic zone where earthquakes occur. Because of tremor's proximity to earthquakes, it is possible that tremor plays a role in earthquake occurrence. Thus, it is important to understand not only where tremor occurs, but also it's behavior in relation to earthquake activity. Ideally, ambient tremor activity could be used to forecast earthquake occcurence if there is a distinct relationship betweent tremor and earthquake occurrence.

Volcanic tremor activity has been observed at volcanoes all over the world. It differs from tectonic tremor in that most volcanic tremor is harmonic and radiates from shallow depths, though it can also occur deeper (30-60 km). Volcanic tremor also can last from minutes to days. Drivers of volcanic tremor are currently under debate. It could be the result of (1) bubble formation, coalescence, and collapse within water or magma, (2) rock fracturing/crack openings, and/or (3) unsteady magma flow.

Please feel free to contact me about future collaborations regarding this topic. (Send me a message.)




Volcano Seismicity

Active volcanoes are sources of a wide variety of seismic signals. Earthquakes and tremor recorded at volcanoes can provide a wealth of knowledge about the deformation processes beneath the surface. Thus, understanding the sources of these seismic signals is important for mitigating hazard as volcanoes can swell, subdside, crack, emit steam, explode, etc.

Please feel free to contact me about future collaborations regarding this topic. (Send me a message.)