Earthquake-source parameters: Are they what you think they are?

Tristan E. Buckreis, Brian S. Chiou, Robert B. Darragh, Robert W. Graves, & Jonathan P. Stewart

Published September 8, 2024, SCEC Contribution #13828, 2024 SCEC Annual Meeting Poster #169 (PDF)

From depths to rupture representations, earthquake-source parameters listed in ground motion databases are often compiled from a variety of references that may not be compatible with each other. In the process of assembling the Next Generation Attenuation (NGA)-West3 database, careful procedures are being taken to ensure internal consistency of all metadata. For more information about the NGA-West3 project database, please refer to 2024-SCEC abstract “Overview of the NGA-West3 Ground Motion Database” (Buckreis et al. 2024).

One parameter that highlights this dilemma is hypocentral depth (Zhyp). There is no debate that Zhyp is defined as the depth to where the earthquake originates, however how “depth” is defined is not standardized. Some catalogs report Zhyp relative to the WGS84 geoid (i.e., mean sea level), whereas others report Zhyp relative to the ground surface or other datums. As long as the reference datum is known for all catalogs, adjustments can be made to obtain a compatible dataset. More often than not, documentation for this type of information is not presented in catalogs, requiring targeted efforts to produce consistent source metadata.

Finite fault models (FFMs) are another critical component of source characterization that present a different set of challenges. It is becoming more common for many teams of researchers to publish FFMs following significant earthquakes, such as the 2023 Kahramanmaraş, Türkiye earthquakes. These FMMs are used to derive source-to-site distances that are used to develop ground motion models. Ideally, FFMs are developed using a variety of data types (e.g., aftershocks, GPS, InSAR, teleseismic, etc.) including at a minimum local strong ground motions and considering the presence or lack of surface rupture. It is most beneficial when FFM slip distributions are provided in a digital format to facilitate further analysis and processing (e.g., calculation of site distance and other metrics, trimming to remove areas that do not contribute to significant ground motions, comparison among models for same event, etc.). FFMs are not used when they do not satisfy these criteria or do not provide sufficient documentation about their development.

Our recommendation is to increase communication between data-providers and data-users, which is facilitated by engineers participating in science-focused meetings like SCEC-2024 and corollary seismologist engagement in engineering meetings.

Key Words
earthquake, hypocentral depth, finite-fault models, parameters, database

Citation
Buckreis, T. E., Chiou, B. S., Darragh, R. B., Graves, R. W., & Stewart, J. P. (2024, 09). Earthquake-source parameters: Are they what you think they are?. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motions (GM)