Nicholas van der Elst
Science and Products
Operational Earthquake Forecasting – Implementing a Real-Time System for California
It is well know that every earthquake can spawn others (e.g., as aftershocks), and that such triggered events can be large and damaging, as recently demonstrated by L’Aquila, Italy and Christchurch, New Zealand earthquakes. In spite of being an explicit USGS strategic-action priority (http://pubs.usgs.gov/of/2012/1088; page 32), the USGS...
Improving earthquake forecasts during swarms with a duration model
Earthquake swarms present a challenge for operational earthquake forecasting because they are driven primarily by transient external processes, such as fluid flow, the behavior and duration of which are difficult to predict. In this study, we develop a swarm duration model to estimate how long a swarm is likely to last based on actuarial...
Llenos, Andrea L.; Van Der Elst, Nicholas Updated California aftershock parameters
Reasenberg and Jones (1989) introduced a statistical model for aftershock rate following a mainshock along with estimates of “generic” California parameter values based on past aftershock sequences. The Reasenberg and Jones (1989) model has been used for decades to issue aftershock forecasts following M≥5">M≥5...
Hardebeck, Jeanne L.; Llenos, Andrea L.; Michael, Andrew J.; Page, Morgan T.; Van Der Elst, Nicholas Turing-style tests for UCERF3 synthetic catalogs
Epidemic-Type Aftershock Sequence (ETAS) catalogs generated from the 3rd Uniform California Earthquake Rupture Forecast (UCERF3) model are unique in that they are the first to combine a complex, fault-based long-term forecast with short-term earthquake clustering statistics. We present Turing-style tests to examine whether these synthetic catalogs...
Page, Morgan T.; Van Der Elst, Nicholas Accounting for orphaned aftershocks in the earthquake background rate
Aftershocks often occur within cascades of triggered seismicity in which each generation of aftershocks triggers an additional generation, and so on. The rate of earthquakes in any particular generation follows Omori's law, going approximately as 1/t. This function decays rapidly, but is heavy-tailed, and aftershock sequences may persist for long...
Van Der Elst, Nicholas Tidal triggering of earthquakes suggests poroelastic behavior on the San Andreas Fault
Tidal triggering of earthquakes is hypothesized to provide quantitative information regarding the fault's stress state, poroelastic properties, and may be significant for our understanding of seismic hazard. To date, studies of regional or global earthquake catalogs have had only modest successes in identifying tidal triggering. We posit that the...
Delorey, Andrew; Van Der Elst, Nicholas; Johnson, Paul Three ingredients for Improved global aftershock forecasts: Tectonic region, time-dependent catalog incompleteness, and inter-sequence variability
Following a large earthquake, seismic hazard can be orders of magnitude higher than the long‐term average as a result of aftershock triggering. Because of this heightened hazard, emergency managers and the public demand rapid, authoritative, and reliable aftershock forecasts. In the past, U.S. Geological Survey (USGS) aftershock forecasts...
Page, Morgan T.; Van Der Elst, Nicholas; Hardebeck, Jeanne L.; Felzer, Karen; Michael, Andrew J. Fortnightly modulation of San Andreas tremor and low-frequency earthquakes
Earth tides modulate tremor and low-frequency earthquakes (LFEs) on faults in the vicinity of the brittle−ductile (seismic−aseismic) transition. The response to the tidal stress carries otherwise inaccessible information about fault strength and rheology. Here, we analyze the LFE response to the fortnightly tide, which modulates the amplitude of...
Van Der Elst, Nicholas; Delorey, Andrew; Shelly, David R.; Johnson, Paul Induced earthquake magnitudes are as large as (statistically) expected
A major question for the hazard posed by injection-induced seismicity is how large induced earthquakes can be. Are their maximum magnitudes determined by injection parameters or by tectonics? Deterministic limits on induced earthquake magnitudes have been proposed based on the size of the reservoir or the volume of fluid injected. However, if...
Van Der Elst, Nicholas; Page, Morgan T.; Weiser, Deborah A. ; Goebel, Thomas; Hosseini, S. Mehran Larger aftershocks happen farther away: nonseparability of magnitude and spatial distributions of aftershocks
Aftershocks may be driven by stress concentrations left by the main shock rupture or by elastic stress transfer to adjacent fault sections or strands. Aftershocks that occur within the initial rupture may be limited in size, because the scale of the stress concentrations should be smaller than the primary rupture itself. On the other hand,...
Van Der Elst, Nicholas; Shaw, Bruce E. Complex faulting associated with the 22 December 2003 Mw 6.5 San Simeon California, earthquake, aftershocks and postseismic surface deformation
We use data from two seismic networks and satellite interferometric synthetic aperture radar (InSAR) imagery to characterize the 22 December 2003 Mw 6.5 San Simeon earthquake sequence. Absolute locations for the mainshock and nearly 10,000 aftershocks were determined using a new three-dimensional (3D) seismic velocity model; relative...
McLaren, Marcia K.; Hardebeck, Jeanne L.; Van Der Elst, Nicholas; Unruh, Jeffrey R.; Bawden, Gerald W.; Blair, James Luke
The Past Holds the Key to the Future of Aftershock Forecasting
The outcomes of past aftershock sequences can be used to describe the range of possibilities for a current sequence.