Ground Motion Simulation

Calculates a ground acceleration history using a ground motion model written in a python script

Creates a realistic ground motion simulation with given input parameters. The object generates a time-acceleration history using the process outlined in Sabetta et al. (2021). The required function inputs M,R,and Vs30 correspond to the earthquake magnitide, source-to-site distance, and shear wave velocity at a depth of 30m, respectively. F, R_type and n are optional parameters that correspond to the style of faulting, the type of source-to-site distance being used and the random seed to be used. The Magnitude of an event is a measure of its strength, the source-to-site distance is how far from the event we are interested in estimating the ground acceleration at, Vs30 is a soil property that describes the propogation of waves through the soil. There are 3 distinct fault types that can be specified in the function: Strike-Slip, Thrust Fault, and Normal Fault denoted as 'SS', 'TF', and 'NF'. The source-to-site distance can be defined in one of two ways, either as Joyner-Boore distance or Epicentral distance which can be input as 'Rjb' and 'Repi'. The code block below shows the distinction between these two commonly used distance measurements. The function values return in units of (g), so the scale_factor by default is set to 9.81

[Functions<<<{"href": "../../syntax/Functions/index.html"}>>>]
  [groundmotion]
    type = GroundMotionSim<<<{"description": "Calculates a ground acceleration history using a ground motion model written in a python script", "href": "GroundMotionSim.html"}>>>
    M<<<{"description": "Magnitude of Event"}>>> = 7.1
    R<<<{"description": "Joyner-Boore or Epicentral Distance"}>>> = 10
    Vs30<<<{"description": "Shear Wave Velocity at 30m"}>>> = 300
    n<<<{"description": "Random Seed"}>>> = 0
  []
[]

Figure 1: Source-to-site distance measurements

Figure 2 shows simulated ground motion generated from the set of inputs in the above Function block. Varying the seed may provide slightly different results due to the randomly generated phase angles that are used to formulate the time-history, but the frequency domain for a set of inputs remains the same. The central frequency vs time is shown in Figure 3

Figure 3: Central Frequency over Time Domain