Seistech Simulation Atlas

 

Q: What exactly is being shown on this webpage?

This Simulation Atlas product provides a interactive viewing of all the mapped active faults in New Zealand, their properties, and an illustrative ground motion simulation for a potential major earthquake on each fault.

 

Q: What is the reference for all of the earthquake faults?

The set of faults that are displayed are based on Stirling et al. (2012), which is the current national concensus model used to describe seismic hazard across New Zealand.

 

Q: What do the polygons represent?

They represent the surface projection of the fault. The upper edge of the fault (that which is closest to the surface) is shown with a thicker line. Most (but not all faults) have upper edges which are near to the surface, and extend down to depths of 10+ kilometres.

 

Q: What does Tectonic Type represent?

Earthquakes occur in the earths crust due to ruptures on faults Scientifically we typically talk about different Tectonic types within which earthquake ruptures occur. Here we differentiate between faults that occur in Active Shallow Crustal (Crustal), Volcanic, and Subduction interface (Subduction) environments. Active Shallow Crustal earthauakes occur within the shallow crust in areas of active seismicity. Volcanic earthquakes also typically occur in the shallow crustal regions, but in regions of active volcanism (which means the properties of these earthquakes are notably different). Subduction zone earthquakes occur in regions where one tectonic plate is subduced beneath the other subduction interface earthquakes at the interface between the two plates, and subduction slab earthquakes in the subducted slab itself.

 

Q: What does Magnitude represent?

Magnitude (specifically Moment magnitude) is a measure of the size of the earthquake. See https://en.wikipedia.org/wiki/Moment_magnitude_scale

 

Q; What does Probability represent?

We cannot predict precisely when earthquakes will occur on faults. However, using information associated with the present and historical movement of the earth we can forecast the probability of a specific earthquake rupture. The probabilities provided are that in a 50 year period, which is the typical time frame used in the design of structures. A probability of 50% is equivalent to guessing heads in a coin toss, and 17% for a given number of a six-side die, for example.

See: https://en.wikipedia.org/wiki/Earthquake_forecasting

 

Q: What is the difference between fault and rupture?

Fault describes the geometry of the weakness in the crust on which an earthquake rupture can occur. The rupture is the earthquake itself, whereas the fault exists prior to any specific earthquake occurring.

 

Q: What does the image of the fault rupture represent?

When you select a specific fault, an image of a potential rupture on that fault will appear. This rupture image highlights the location where the rupture begins (the hypocentre denoted with a star); the slip amplitude that occurs due to rupture over the fault (with warmer colours indicating higher slip).

 

Q: How do you know the specific rupture that will occur on each fault?

We dont! This is only one potential rupture that could occur on the fault, there is uncertainty in the exact rupture that will occur during the next earthquake in rigorous we consider many possibilities for potential future ruptures. Only one example for each fault is provided in this interfactive product, because it is focused on general science communication, and not rigorous quantiative analysis.

 

Q: What specifically is displayed in the ground motion simulation animation?

For each rupture, a ground motion simulation animation is provided via YouTube. The animation begins with showing the image of the fault rupture from a rotating perspective (see: Q: What does the image of the fault rupture represent?). As the animation begins it illustrates both the occurrence of rupture slip on the fault (right colorbar) and also the consequent ground motion at the earths surface in terms of the peak ground velocity (left colorbar). These animations are based on ground motion simulation models which solve the physics-based equations that describe earthquake rupture and ground motion wave propagation much in the same way that similar models are used in weather prediction. The animations are created using the GmSimViz open-source software (Polak et al. 2019).

 

Q: Who has supported the development of Simulation Atlas?

This open-source product has been developed by SeisTech in partnership with QuakeCoRE: The New Zealand Centre for Earthquake Resilience. QuakeCoRE researchers performed the underlying ground motion simulations, which were calculated using high-performance computing resources provided by the National e-Science Infrastructure (NeSI). Historical earthquake data depicted is provided by GeoNet.

 

References:

 

Stirling, M. et al. National seismic hazard model for New Zealand: 2010 update. Bulletin of the Seismological Society of America 102, 15141542 (2012).

Polak, V. & Zhu M, Bae S, Motha J, Bradley BA, Razafindrakoto HNT. GmSimViz: Automated 3D visualization of ground motion simulation with generic mapping tools (GMT). The Journal of Open Source Software 4, 808 (2019).