SCEC Award Number 12012 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title The Length to which an Earthquake will go to Rupture: Information Gathering
Investigator(s)
Name Organization
Steven Wesnousky University of Nevada, Reno Glenn Biasi University of Nevada, Reno
Other Participants Alex Morelan - Graduate Student4
SCEC Priorities 4e, 3c, 4c SCEC Groups WGCEP, FARM
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 Empirical observations are a critical tool for placing observational bounds on physical models of the earthquake process and on estimates of the length of rupture expected to occur on mapped faults. We have previously used published maps to define the size and number of fault discontinuities at the ends and within historical earthquakes. The work resulted in (1) an empirical upper limit for strike-slip earthquakes of about 4-5 km step-over dimension (2) and the observation that the number of strike-slip ruptures is a decreasing function of the number of step-overs spanned by the rupture. The latter observation provides a statistical basis to estimate the likelihood of an earthquake spanning step-overs in fault trace. In this research we use published accounts of earthquakes that post-dated the previous work and earthquakes not previously included to extend the dataset of strike-slip earthquakes and to gather enough observations to apply the same approach to normal and reverse type earthquakes. We find that the same upper limit of 4-5 km step-over is observed among the newly added strike-slip earthquakes, but that ruptures are observed to propagate across step-overs of 7-8 km for dip-slip earthquakes. As for strike-slip earthquakes, the relative frequency of normal and reverse earthquake ruptures is a decreasing function of the number of step-overs spanned by the rupture. A manuscript summarizing these new data and relations is being prepared.
Intellectual Merit The primary method for studying the macroscopic mechanics of earthquakes is through the use of physics-based computer models. These models are increasingly being used to understand the physical role of fault geometry in limiting the length of earthquake ruptures. Model results, however, span a wide range, because of the number of adjustable parameters, and the parameterization itself. The intellectual merit of this research stems from the development of empirical observations to constrain inputs and help evaluate results from physics-based computer model intended to describe the earthquake source.
Broader Impacts SCEC focuses on earthquake systems science for understanding earthquake physics and applying that understanding to risk reduction in California, with extensions worldwide. Empirical relations from this research will contribute to evaluation of current earthquake rupture forecasts (e.g., UCERF 3), and to the development of future earthquake rupture models. Hazard analysis requires understanding the likely sizes of earthquakes that may occur, and their propensity to jump from fault to fault. This understanding will contribute directly not just to the study of fault physics, but to reducing the uncertainties and improving the quality of seismic hazard estimates in California.
Exemplary Figure Figure 2. Results from a) strike-slip, b) normal and c) reverse type earthquakes. Text in red indicates new observations uncovered in this study. Left side of each figure: Earthquakes are labeled and arranged on the lower axis according to rupture length. Above the label of each earthquake there is a vertical line along which symbols are placed to represent the dimension (vertical axis) of the discontinuities through which the respective earthquake ruptured through (open symbols) or at which it stopped (closed symbols). Right side of figure: Histograms showing the number of earthquake ruptures as a function of the number of step-overs spanned by the rupture. Each is fit to a geometric probability density function. Credits: A. Morelan, UNR graduate student, S. Wesnousky, and G. Biasi.