SCEC Project Details
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) 


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 strikeslip earthquakes of about 45 km stepover dimension (2) and the observation that the number of strikeslip ruptures is a decreasing function of the number of stepovers spanned by the rupture. The latter observation provides a statistical basis to estimate the likelihood of an earthquake spanning stepovers in fault trace. In this research we use published accounts of earthquakes that postdated the previous work and earthquakes not previously included to extend the dataset of strikeslip 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 45 km stepover is observed among the newly added strikeslip earthquakes, but that ruptures are observed to propagate across stepovers of 78 km for dipslip earthquakes. As for strikeslip earthquakes, the relative frequency of normal and reverse earthquake ruptures is a decreasing function of the number of stepovers 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 physicsbased 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 physicsbased 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) strikeslip, 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 stepovers spanned by the rupture. Each is fit to a geometric probability density function. Credits: A. Morelan, UNR graduate student, S. Wesnousky, and G. Biasi. 