DEEP-trigger: Preparation of Subduction Earthquakes: Slow, Deep, Large-scale trigger

The DEEP-trigger project

Subduction zones host the world’s largest earthquakes and tsunamis. Understanding how such earthquakes initiate and interact is a first-order challenge in earth sciences.

The objectives of the DEEPtrigger project is to study subduction zones recently affected by megathrust events or earthquakes sequences, with an enlarged perspective, considering the mechanisms of deformation in the larger subduction system, including the slab, and their potential role in pushing the megathrust to failure.

The project relies primarily on two types of observables:

• Seismological data

• Geodetic data (GNSS)

Processing of GNSS data using PPP with GipsyX, as part of the project

Data

As part of the ERC DEEP-trigger project, we have organised a large-scale GNSS data processing operation specifically dedicated to the region of South America and Mexico. This data, in the form of daily observation files in RINEX format, sampled at 30- or 15-second intervals, comes from various sources, including public institutions, research laboratories and other relevant entities. To facilitate its management, we have organised this data according to its origin, as shown in the table below.

Table 1 : Statistics on data processed as of April 2026:

The total number of stations processed as part of this project amounts to over 2,600, distributed as shown in the graph below.

Station distribution

Processing

Data processing is based on the use of the Precise Point Positioning (PPP) method, using the GipsyX software developed by the Jet Propulsion Laboratory. This advanced method aims to determine the geographical positions of the stations with a high degree of accuracy. It involves a meticulous analysis of the signals transmitted by satellites in Earth orbit, taking into account numerous parameters, such as atmospheric corrections, precise satellite orbits and other potential sources of error. The data processing procedure therefore requires the application of sophisticated mathematical models to achieve a final high-precision position. It should be noted that this processing is generally carried out several weeks after data acquisition, pending the availability of the final products. The parameters used for this processing are listed in the table below:

Table 2: Processing parameters

Time series analysis

As the Earth is subject to various geophysical movements, the calculated positions are also subject to these fluctuations. In order to make optimal use of our data and fully understand the impact of each factor on our stations, we undertake an in-depth analysis of the position time series computed for these stations. This analysis aims to identify, quantify and understand influential phenomena, such as earthquakes, annual and semi-annual components, post-seismic aftershocks, antenna changes, as well as other significant events. To carry out this process, we use ITSA, a software package specially developed in-house for this purpose.

Example of a time series analysed using ITSA

The results of the analyses carried out, as well as statistical data relating to the stations analysed, are made available via an interactive map specifically designed for this purpose.

Using this dedicated interactive interface, users can easily and intuitively view the results of the various analyses carried out, whilst having privileged access to statistical information relating to the stations concerned. This interactive map is a key tool for making data and results available, providing an optimal user experience when navigating and exploring this valuable information.

Table 3: Software used

See also the project website.