Investigating volcano tectonic interactions in the Natron Rift of the East African Rift System
Jones, Joshua Robert
MetadataShow full item record
Continental rifting, like other plate tectonic processes, plays a large role in shaping the Earth's crust. Active rift zones evolve from repeated tectonic and magmatic events including volcanic activity. Through investigations of currently and previously active rifts, scientists have discovered considerable interactions between these tectonic and magmatic processes during a rift's evolution; however questions remain about these interactions especially in youthful stages of rifts. We investigate an early phase magma-rich section of the East African Rift System (EARS), named the Eastern Branch to assess volcano-tectonic interactions. The Eastern Branch of the EARS consists of volcanically rich rifts that are actively spreading the Nubian Plate, Somalian plates, and Victoria block at different evolutionary stages making it an ideal study area for volcano-tectonic interactions. Our initial investigation of active volcano-tectonic interactions centered on a rifting event that occurred between 2007-2008 in the Natron Rift, a rift segment in the southern Eastern Branch located in Northern Tanzania. This rifting event contained multiple occurrences of tectonic, magmatic, and volcanic activity in close proximity. We examine the stress transferred from these events to the Natron Fault, which is the major border fault in the area, with analytical modeling using the USGS program Coulomb 3.4. We processed Global Positioning System (GPS) data that recorded slip on the major border fault in the region in early January 2008 and test which events could generate large enough stress changes to trigger the observed slip using a previously defined threshold of 0.1 MPa. These initial models were created using simplified model parameters, such as an elastic homogeneous half-space, and find that 1) magmatically induced stress perturbations have the potential to trigger fault slip on rift border faults, 2) magmatic events have the potential to trigger strike‐slip motions on a rift border fault, and 3) the proximity of magmatic activity may affect occurrences of slip on adjacent border faults. We then further investigate volcano-tectonic interactions in the Natron Rift by testing using numerical modeling with the CIG finite element code PyLith. We systematically test how adding topography, heterogeneous materials, and various reservoir volumes to a deflating 3 km deep magma reservoir system at the active volcano Ol Doinyo Lengai can affect stress transfer to the adjacent Natron Fault. We compare eight models with variations in topography, material properties, and reservoir volumes to calculate the percent differences between the models; to test their effects on the stress change results. We find that topography plays the largest role with the effect increasing with reservoir size. Finally, we seek to improve the capability of investigating volcano-tectonic interactions in the Natron Rift at faster time- scales by improving Global Navigation Satellite System (GNSS) positioning data (latitude, longitude, and height) collection and distribution capabilities. In the final part of this work, we describe a new Python-based data broker application, GNSS2CHORDS, that can stream real-time centimeter precision displacement data distributed by UNAVCO real-time GNSS data services to an online EarthCube cybertool called CHORDS. GNSS2CHORDS is applied to the TZVOLCANO GNSS network that monitors Ol Doinyo Lengai in the Natron Rift and its interactions with the adjacent rift border fault, the Natron Fault. This new tool provides a mechanism for assessing volcano-tectonic interactions in real-time. In summary, this work provides a new avenue for understanding volcano-tectonic interactions at unprecedented, 1-second time-scales, demonstrates slip can be triggered by small stress changes from magmatic events during early phase rifting, and provides insights into the key role of volcanic topography during volcano-tectonic interactions.
General Audience Abstract
Investigating interactions between active volcanoes and tectonics (fault zones) is important for understanding how continental rifts grow and evolve over time. Modern researchers use geodetic data, geologic models, and computer simulations of rift processes; like volcanic eruptions and fault movement; to understand how stress in transferred and material deforms due to rift activity. We are especially interested in understanding the stress interactions when volcanic eruptions and earthquakes happen together over a short time period. Our projects apply these tools to examine a segment of the largest active continental rift zone, the Natron Rift in the East African Rift System (EARS), to understand more about the details of these volcano-tectonic interactions when continents break apart (rifting). We first present results that stress transferred to the Natron Fault associated with magmatic activity from the volcano Ol Doinyo Lengai may trigger a major fault to move. Next, we continue our investigations into volcano-tectonic interactions by seeing how volcanic properties could affect stress transferred in the Natron Rift region. We choose to initially test stress variations associated with different 1) topography surfaces, 2) material properties, and 3) reservoir volumes associated with the volcano Ol Doinyo Lengai using a more advanced computer modeling approach. This deeper investigation provides information about the individual roles these parameters play in a younger rift region. We present results that topography has the most influence on the stress transferred to the Natron Fault in our models, and that the other parameters did not play a large role in influencing the stress transferred. Finally we work to increase the ability for researchers to perform geodetic studies in the Natron Rift by providing a new method to share surface displacement data at an unprecedented 1 position a second rate (near real-time). This new method is a data broker application called GNSS2CHORDS that can stream cm precision displacement data to an online cybertool called CHORDS. With our models and data provided through open source methods this work contributes significantly to our understanding of volcano-tectonic interactions.
- Doctoral Dissertations