# CyberShake Background Seismicity

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Jump to navigationJump to search**Goal: determine the importance of background seismicity in different parts of CA to either validate it's exclusion in CyberShake or motivate an inclusion strategy.**

## UCERF2

To illustrate what events UCERF2 includes in background seismicity, below are plots of the magnitude-frequency distribution for the UCERF2 ERF in both linear and log scale. Blue is the full UCERF2 distribution, and black is the on-fault ERF used in CyberShake. All UCERF2 finite-fault ruptures are included in CyberShake, regardless of magnitude, though the GR distribution applied to type B faults is only for M>=6.5, and floating rupture sources start at M6.5, which is why there are fewer CyberShake events for M<6.5.

Calculation parameters:

- GMPE: NGA-West2 GMPE (average of 4 models)
- ERF: UCERF2, with and without background seismicity
- Site Effects: Vs30 is from Wills (2015), no basin depth terms included
- IMT: 2 second SA.

Model | 10% in 50yr | 2% in 50yr | 1% in 50yr |
---|---|---|---|

Excluding Background | |||

Including Background | |||

Ratio Exclude/Include |

## UCERF3

Calculation parameters:

- GMPE: NGA-West2 GMPE (average of 4 models)
- ERF: UCERF3, with the following configurations
- Supra-seismogenic ruptures only (only supra-seismogenic ruptures have finite fault surfaces in UCERF3, all others treated as gridded)
- Supra and Sub-seismogenic ruptures only (this adds gridded ruptures that correspond to sub-seimogenic ruptures on known faults)
- Supra, Sub-seismogenic, and off fault ruptures (complete model)

- Site Effects: Vs30 is from Wills (2015), no basin depth terms included
- IMT: 2 second SA.

Model | 10% in 50yr | 2% in 50yr | 1% in 50yr |
---|---|---|---|

Supra-Seismogenic On-Fault Only | |||

Sub+Supra-Seismogenic On-Fault Only | |||

Complete Model (Supra+Sub+Off) | |||

Ratio Supra-Only/Complete | |||

Ratio Supra+Sub/Complete |