Research Opportunity Description
Earthquakes are well-known to cluster in space and time, evolving as sequences of events. Earthquake clustering models underly critical USGS products such as the National Seismic Hazard Model (NSHM) and Operational Aftershock Forecasts (OAF). Despite this broad tendency towards clustering, sequence evolution varies dramatically from region to region and sequence to sequence. Earthquake sequences are commonly described within two main categories: “mainshock-aftershock” and “swarm” sequences. Although these descriptions are convenient, they describe only endmember behaviors, with large observed variations in aftershock productivity, active timescales, and magnitude evolution. And because earthquake sequences can occur in populated areas, they inspire public interest as well as possible anxiety stemming from uncertainty around what may happen next. Earthquake sequences and how they are treated in seismic hazard forecasts therefore represent an important target for further research, both scientifically and societally.
Efforts are underway within the USGS to develop new tools to communicate and forecast earthquake sequence evolution, including OAF and new web products that characterize earthquake sequences. Lessons learned during the recent 2023 50-state NSHM and 2025 Puerto Rico and Virgin Islands NSHM updates also suggest that seismic hazard forecasts can be improved by better modeling of earthquake sequences (aftershocks and swarms alike) and accounting for regional variations in earthquake occurrence. Research under this Opportunity is envisaged to complement and support these ongoing efforts to improve USGS forecasts and could include research into earthquake sequence source physics, earthquake sequence near-real-time characterization, earthquake sequence statistics, and/or impacts on seismic hazard forecast products, as outlined below.
Earthquake sequence physics
Research into earthquake sequence physics encompasses a wide range of sub-topics, including the physical conditions in the source zones of earthquake sequences (e.g., geology, fluids, temperature, stress), evolution of these conditions during a sequence, role of aseismic slip, and/or interactions among individual earthquakes through stress changes or other processes. What factors control tendencies for mainshock-aftershock versus swarm sequences? What factors control earthquake aftershock productivity? Which conditions can be characterized either prior to or during the early stages of a sequence, and which have the greatest influence on sequence evolution? Earthquake sequence physics research could be conducted via high-resolution analysis of earthquake sequences, systematic comparisons among previously analyzed earthquake sequences, or many other approaches.
Earthquake sequence near-real-time characterization
Research into improved methods of near-real-time characterization of earthquake sequences could include techniques to rapidly produce more complete and consistent earthquake magnitudes or characterize faulting structure or source migration by high-resolution source locations or focal mechanisms. Machine learning or other approaches could be utilized toward to achieve these goals. Research could include benchmarking rapid analyses against later post-processed high-resolution earthquake catalogs.
Earthquake sequence statistics
Research into the statistics of earthquake sequence evolution could include methods to forecast the magnitude and/or time evolution of sequences that deviate from idealized mainshock-aftershock behavior. Such sequences include swarm-like sequences (those lacking a clear mainshock and decaying aftershock sequence), nested sequences (for example, a swarm within an aftershock sequence), and/or long-duration sequences lasting years to decades. Research into mainshock-aftershock sequences could include developing regional parameter sets and characterizing deviations from standard models, such as the Epidemic-Type Aftershock Sequence model (ETAS), to make improvements to statistics-based aftershock forecasts as well as the NSHM, which relies on these models for declustering to obtain a long-term background seismicity rate. Investigations might also involve examining the consequences of incompleteness or magnitude biases that are often present in catalogs and affect the estimation of the Gutenberg-Richter b-value, a critical parameter for forecasting.
Impact on seismic hazard forecasts
Research into how earthquake sequence statistics and regional variations impact USGS hazard products could include testing the influence of variations in sequence statistics such as b-values and productivity on current hazard models, developing regional earthquake catalogs with consistent statistical behavior for the NSHM, and exploring how this research could be implemented in future hazard model updates such as the 2026 Guam and American Samoa update and 2029 50-state update. Research into regionalized parameters, particularly for the ETAS model, is critical for the future development of nationwide time-dependent Operational Earthquake Forecasting, to produce consistent seismic hazard forecasts from the short timescales currently covered by OAF to the long timescales covered by the NSHM. Research could thus also include developing and maintaining the consistency of earthquake sequence/clustering models over the wide range of timescales covered by USGS forecasting products.
Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.
Proposed Duty Station(s)
Golden, Colorado
Moffett Field, California
Areas of PhD
Seismology, geophysics, geodesy, geology, engineering, mathematics, physics, computer science, statistics, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).
Qualifications
Applicants must meet one of the following qualifications: Research Geophysicist, Research Geologist, Research Statistician, Research Computer Scientist, Research Geodesist, Research Civil Engineer, Research Engineer, Research Physicist, or Research Mathematician.
(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)
