Author Topic: EQHazard: dm input value for ERF  (Read 4803 times)

Anne Hulsey

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EQHazard: dm input value for ERF
« on: April 21, 2020, 12:44:33 AM »
Currently, the ERF output assumes that the magnitude interval for the OpenSHA catalog is 0.1. Can that become an input parameter so I can decrease it to 0.05?

Anne Hulsey

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Re: EQHazard: dm input value for ERF
« Reply #1 on: April 22, 2020, 10:00:14 PM »
A recent discussion with Jack Baker indicated that there might also be an OpenSHA input parameter to specify the empirical relationships for moment magnitude to rupture geometry (e.g. Wells and Coppersmith 1994).

This would also be a nice feature (that I would use if it were included within the next 2 months) but the parameter for dm is a higher priority.

elhaddad

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Re: EQHazard: dm input value for ERF
« Reply #2 on: April 29, 2020, 02:54:13 PM »
Thanks for the feature requests!
We will consider them in the near future and will keep you posted on any progress.

elhaddad

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Re: EQHazard: dm input value for ERF
« Reply #3 on: May 28, 2020, 01:09:14 AM »
We started looking into implementing these features. I found that in OpenSHA UCERF implementations the magnitude interval is not one of the adjustable parameters.

For instance you can check here:
https://github.com/opensha/opensha-core/blob/3ca5a46ae92589c4d15e4e9a1d5110658e58a687/src/org/opensha/sha/earthquake/rupForecastImpl/WGCEP_UCERF_2_Final/UCERF2.java

line 68 shows that the variable DELTA_MAG is declared as final, which means its value cannot be changed for UCERF2.

Selecting the magnitude area relationship is possible.
The possible values are:
Ellsworth-A (WGCEP, 2002, Eq 4.5a)
Ellsworth-B (WGCEP, 2002, Eq 4.5b)
Hanks & Bakun (2002)
Somerville (2006)
WGCEP (2007) power law
Shaw (2007)

Wells and Coppersmith 1994 model is not one of the allowed models for UCERF2.

Specifying the magnitude area relationship is not possible using the current Mean UCERF2 model.
But it is possible to add the adjustable UCERF2 model as a possible input.
Just wanted to confirm with you that this is the feature you are looking for before implementing it.

elhaddad

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Re: EQHazard: dm input value for ERF
« Reply #4 on: May 28, 2020, 05:27:43 PM »
 I forgot to mention in OpenSHA website, there is some description of the magnitude area relationships, in this page:
http://www.opensha.org/glossary-magScalingRelation

Anne Hulsey

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Re: EQHazard: dm input value for ERF
« Reply #5 on: May 28, 2020, 08:34:19 PM »
Thank you for tracking down documentation on the dm and on the magnitude area relationships. I am satisfied with these responses. While I still think the magnitude area input would be a great feature to have, I suggest de-prioritizing it. I personally would not use it since Wells and Coppersmith is not an option for UCERF2.

elhaddad

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Re: EQHazard: dm input value for ERF
« Reply #6 on: May 29, 2020, 11:54:36 PM »
For you or others who might be interested in the future, it is now possible to use the adjustable UCERF2 version and set the magnitude area relationship as follows:

   "EqRupture": {
      "Type": "ERF",
      "RuptureForecast": "WGCEP Eqk Rate Model 2 ERF",
      "Parameters":{
         "Mag-Area Relationship": "Somerville (2006)"
      }
   }

This is supported by the latest preview release (v1.1.1):
https://github.com/NHERI-SimCenter/GroundMotionUtilities/releases/tag/v1.1.1

Anne Hulsey

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Re: EQHazard: dm input value for ERF
« Reply #7 on: June 03, 2020, 12:52:05 AM »
Nice update. Thanks!

elhaddad

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Re: EQHazard: dm input value for ERF
« Reply #8 on: June 03, 2020, 01:03:54 AM »
Just to clarify, although DELTA_MAG is not an adjustable parameter, that does not mean the value cannot be changed.
However to change it we will need to have a custom build of OpenSHA.
In other words, the value is fixed within a build.
If you are interested to do that, we can look into building a custom OpenSHA from source.
Only issue, it is not going to be a build that we can reuse.
You can also check any of the OpenSHA apps to see which ERFs are available and what parameters can be adjusted.
It is possible that other ERFs or other parameters may achieve what you need.

Anne Hulsey

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Re: EQHazard: dm input value for ERF
« Reply #9 on: June 03, 2020, 01:17:59 AM »
Thanks for the follow up. For context, here is my discussion with Jack Baker regarding the benefit of a variable DELTA_MAG value. At this point in time, I do not foresee pursuing this any further.
With regards to looking up the parameters for other ERFs, I may return to the question of mag-area relationships later. Thank you for the tip.

Anne:
I wanted to follow up on my question from the presentation regarding whether each scenario is sampled multiple times.
 
Iím wondering what would be lost if you donít use multiple samples. My gut reaction is that if you have one rupture that controls the lower tail of the hazard curve, you would have trouble if you end up taking a single realization that is either really low or really high. Taking many samples would do a better job of P(Y>y|scenario). The counter to that concern would be that if you really have all the scenarios represented, you should have pretty similar scenarios that even out the problem of using only one sample per scenario. (E.g. 7.8 and 7.9Mw on San Andreas)
 
Did Mahalia find that using a single sample was comparable to using multiple samples?


Baker:
Good question, and it seems like you have a pretty good handle on it. In general, I would say that there's not a lot of benefit to generating multiple ground motion samples per rupture. More samples can give better resolution of the tail. But I you want more samples, I would prefer to sample more ruptures as well.

That said, the OpenSHA rupture generator actually discretizes the possible ruptures instead of doing a traditional Monte Carlo sampling. So getting more ruptures entails changing some of the OpenSHA parameters (e.g., sampling magnitudes in intervals of 0.05 instead of 0.1). So Mahalia decided that a convenient way to get more samples was just to keep her basic set of ruptures and sample multiple ground motions per rupture. It was a fine thing to do, but I would call it a pragmatic choice rather than a theoretically necessary choice.