Anyone who has taken an introductory earth science class knows that the earth has 3 main layers: the core, the mantle, and the crust, and that these are composed of even more smaller-scale layers. But drilling through the earth is expensive, difficult, and is limited to only the upper crust, so how exactly do scientists study the structure of the earth beyond the first couple kilometers? The key lies in earthquakes. By studying the way earthquake energy travels through the earth, seismologists are able to model its layers and their properties, namely the speed at which earthquake waves travel through them.
The research project I am currently working on aims to reconstruct the generalized 1 dimensional structure of the Cordillera Talamanca mountain range in southern Costa Rica. Costa Rica sits on top of a subduction zone, meaning that the ocean crust is being pulled below the overriding continental crust. The overriding plate in subduction zones typically experiences frequent, powerful earthquakes and is covered by volcanoes. While the northern half of Costa Rica, whose structure is well understood, has a structure consistent with sitting atop a subduction zone, the southern half of the country lacks deep earthquakes and a volcanic arc. Few studies have been done to determine the crustal structure below the Talamancas and why it is so anomalous.
For my project, I am working with earthquake data from the last 8 years from 3 regions outside of the borders of Costa Rica. The earthquakes used are relatively strong (magnitude 4.5 or above), which ensures that their signals are distinct and are picked up by many seismic sensors within Costa Rica. My role so far has been looking at the digitized signals of each earthquake from each sensor and marking the first arrival of the earthquake for each sensor’s recording. Since the software we use knows the exact location of each sensor and, using my picked first arrivals, knows the time at which the earthquake’s energy first arrived at each sensor, it is able to locate the source location, beginning time, and depth of each earthquake. I aim to create various models using the first arrival times of the earthquake at each sensor by adjusting different properties of the earth (particularly the depth of different “layers” and the speed earthquake waves travel through it) until I find a model that fits the data the best.
This work aims to use earthquake data to complement existing models of Costa Rican crustal structure and to create a model which accounts for the unique structure of the southern half of the country. In addition, this work may help determine which existing model can explain the seismological observations. Our project holds significance for the RSN (the national seismological network of Costa Rica), as a new velocity model of the layers beneath southern Costa Rica will enable them to locate earthquakes more precisely.