The Attenuation Relationship Plotter is a specific graphical user interface (GUI) application bundled within OpenSHA (Open Seismic Hazard Analysis), a prominent open-source, Java-based platform used to conduct Probabilistic Seismic Hazard Analysis (PSHA).
Its core purpose is to allow seismologists, civil engineers, and hazard analysts to visualize and compare Ground Motion Prediction Equations (GMPEs), which are mathematically modeled formulas explaining how earthquake shaking intensity decreases (attenuates) as it travels away from a fault line. Key Features and Capabilities
Model Selection: Users can choose from a vast database of pre-built empirical models, including the industry-standard Next Generation Attenuation (NGA) West 2 datasets.
Intensity Measure Types (IMT): The tool plots various metrics of earthquake shaking severity, such as Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Spectral Acceleration (SA) over different periods.
Y-Axis Parameters: The plotter can calculate and display several statistical outputs: Median/Mean ground motion prediction values. Standard Deviation (aleatory uncertainty).
Exceedance Probability for a designated Intensity Measure Level (IML). IML at a specified exceedance probability.
X-Axis Independent Variables: You can set any numerical parameter supported by the chosen model as the independent variable on the horizontal axis (most commonly distance from the rupture or earthquake magnitude). How It Operates
The plotter functions as an interactive calculator where you isolate one variable and fix the others to see a resulting curve. For example, if you map PGA vs. Distance along the X-axis, the interface prompts you to fill in rigid numeric constraints on the bottom right for other conditions the model relies on. These constraints include: Moment Magnitude ( MWcap M sub cap W ) of the simulated earthquake. VS30cap V sub cap S 30 end-sub
values (the average shear wave velocity in the top 30 meters of soil, which distinguishes hard rock from soft soil). Fault geometry details like the rake angle or dip angle.
Once these values are populated, clicking “Add Curve” commands the engine to graph the data. Users can layer multiple curves over one another, making it easy to compare how different global seismological models evaluate the exact same fault scenario.
If you are using this tool for a specific engineering study, let me know:
Which seismic region or source you are evaluating (e.g., California crustal vs. a subduction zone) Which specific ground motion model (GMPE) you plan to use The specific intensity metrics (PGA or SAcap S sub cap A ) required for your building criteria
I can provide more targeted details or step-by-step guidance.
Attenuation Relationship Plotter – Plotting magnitude on X-axis