alaska_2007_intro [GEM Hazard Team Wiki]

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====== The 2007 USGS Alaska Seismic Hazard Model ======

The 2007 USGS Alaska seismic hazard model is described by [[alaska_2007_intro#References|Wesson et. al. (2007)]] (see also [[http://earthquake.usgs.gov/hazards/?source=sitenav|the USGS Website]]). Here we present a short description of the OpenQuake-engine implementation of the model.

===== The Seismic Source Model =====
The seismic source model consists of different seismic source typologies to describe earthquake occurrence in different tectonic settings. The model defines gridded seismicity to model both active shallow and deep intraslab seismicity. Fault sources are instead defined for shallow crustal faults and large subduction interface events. Gridded seismicity models are implemented as collections of NRML [[https://github.com/gem/oq-nrmllib/blob/master/examples/source_model/point-source.xml|pointSource]] objects. Crustal faults and subduction faults are instead modeled as NRML [[https://github.com/gem/oq-nrmllib/blob/master/examples/source_model/simple-fault-source.xml|simpleFaultSource]] and NRML [[https://github.com/gem/oq-nrmllib/blob/master/examples/source_model/complex-fault-source.xml|complexFaultSource]] objects, respectively.\\

The whole source model is divided into the following sub-models:
  * Active shallow crust gridded seismicity
  * Subduction intraslab gridded seismcity
  * Active shallow crust faults
  * Subduction interface faults
The map below depicts the annual occurrence rate per source (between minimum and maximum magnitudes) for the different source models included in the hazard model. Click the //show map layers// icon to view different source models and base layer maps.

<olmap id="olmap" width="900px" height="500px" lat="60.0" lon="-135." zoom="3" statusbar="1" toolbar="1" controls="1" poihoverstyle="0" baselyr="osm road" gpxfile="" kmlfile="" geojsonfile="">
</olmap>

<olmap_osmlayer id="olmap" name="ASC_point Model" url="http://tilestream.openquake.org/v2/hazard_ALS07_input_asc_point/${z}/${x}/${y}.png" visible="true" attribution="Alaska 2007 Grid (shallow) Model"></olmap_osmlayer>

<olmap_osmlayer id="olmap" name="SubIntraSlab_point Model" url="http://tilestream.openquake.org/v2/hazard_ALS07_input_subintraslab_point/${z}/${x}/${y}.png" visible="true" attribution="Alaska 2007 Grid (deep) Model"></olmap_osmlayer>

<olmap_osmlayer id="olmap" name="ASC_fault Model" url="http://tilestream.openquake.org/v2/hazard_ALS07_input_asc_simplefault/${z}/${x}/${y}.png" visible="true" attribution="Alaska 2007 Active Shallow Crust Fault Model"></olmap_osmlayer>

<olmap_osmlayer id="olmap" name="SubInterface_complexfault Model" url="http://tilestream.openquake.org/v2/hazard_ALS07_input_subinterface_complexfault/${z}/${x}/${y}.png" visible="true" attribution="Alaska 2007 Subduction Interface Fault Model"></olmap_osmlayer>

<html>
<div class='my-legend'>
<div class='legend-title'>Total occurrence rate <br> (number of events / year)
<div class='legend-scale'>
  <ul class='legend-labels'>
<li><span style='background:rgb(30, 92, 179);'></span>< 1e-6</li>
<li><span style='background:rgb(25, 181, 241);'></span>1e-6 - 1e-5</li>
<li><span style='background:rgb(0, 255, 255);'></span>1e-5 - 1e-4</li>
<li><span style='background:rgb(100, 229, 50);'></span>1e-4 - 1e-3</li>
<li><span style='background:rgb(255, 255, 0);'></span>1e-3 - 1e-2</li>
<li><span style='background:rgb(252, 199, 7);'></span>1e-2 - 1e-1</li>
<li><span style='background:rgb(255, 128,  0);'></span>1e-1 - 1</li>
<li><span style='background:rgb(255, 0, 0);'></span>1 - 10</li>
<li><span style='background:rgb(255, 0, 255);'></span>>= 10</li>
  </ul>
</div>
</div>
</div>

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    font-size: 80%;
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    line-height: 18px;
    margin-bottom: 2px;
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    display: block;
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    width: 30px;
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    border: 1px solid #999;
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  .my-legend .legend-source {
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===== The Ground Motion Model =====
The ground motion model distinguishes between three main tectonic regions:
  * Active Shallow Crust
  * Subduction Interface
  * Subduction Intraslab
For each tectonic region, the model considers multiple ground motion prediction equations organized in a logic tree structure.

|< 25em 80% >|
| **Active Shallow Crust**                | **Weight**  |
| [[http://docs.openquake.org/oq-hazardlib/stable/gsim/boore_1997.html
|Boore et. al. 1997]]                 | 0.25       |
| [[http://docs.openquake.org/oq-hazardlib/stable/gsim/sadigh_1997.html
|Sadigh et. al. 1997]]             | 0.25       |
| [[http://docs.openquake.org/oq-hazardlib/stable/gsim/abrahamson_silva_1997.html
|Abrahamson and Silva 1997]]                   | 0.25       |
| [[http://docs.openquake.org/oq-hazardlib/stable/gsim/campbell_bozorgnia_2003.html
|Campbell and Bozorgnia 2003]]                   | 0.25       |
 
|< 25em 80% >|
| **Subduction Interface**                | **Weight**  |
| [[http://docs.openquake.org/oq-hazardlib/stable/gsim/youngs_1997.html
|Youngs et. al. 1997]]                             | 0.5        |
| [[http://docs.openquake.org/oq-hazardlib/stable/gsim/sadigh_1997.html
|Sadigh et. al. 1997]]             | 0.5       |

|< 25em 80% >|
| **Subduction Intraslab**                | **Weight**  |
| [[http://docs.openquake.org/oq-hazardlib/stable/gsim/youngs_1997.html
|Youngs et. al. 1997]]                             | 0.5        |
| [[http://docs.openquake.org/oq-hazardlib/stable/gsim/atkinson_boore_2003.html
|Atkinson and Boore 2003]]          | 0.5        |
=== Reference site condition ===
The NEHRP B/C site condition is assumed to be the reference site conditions for the 2007 Alaska National Seismic Hazard Model. This is equivalent to a Vs30 (shear wave velocity in the uppermost 30 meters) = 760 m/s. GMPEs that do not depend on Vs30 are used with coefficients corrected for the B/C site condition.

===== Hazard Results =====
==== Hazard maps ====
The figures below represent hazard maps for peak ground acceleration, for 10% and 2% probabilities of exceedance  in 50 years , using the OpenQuake-engine.\\
{{:oq_map_alaska_pga_0.1.png?direct&450|}}
{{:oq_map_alaska_pga_0.02.png?direct&450|}}
\\
==== Comparison against USGS results ====
The figures below shows hazard maps, for 10% probability of exceedance in 50 years, provided by the USGS and computed with the OpenQuake-engine. A difference map is also shown which allows to more quantitatively appreciate the differences between the two maps. The largest differences are associated with subduction fault sources. Differences may be due to different approaches in modeling earthquake ruptures in complex geometries and magnitude scaling relationships. Further analysis is required to better constrain what are the sources of the discrepancies.\\
{{:usgs_ak_gm_0p0s_10p50_2007.png?direct&450|}}
{{:oq_map_alaska_pga_0.1.png?direct&450|}}
{{ :abs_diff_map_alaska_pga_0.1.png?direct&450 |}}

===== References =====
  * Wesson, Robert L., Boyd, Oliver S., Mueller, Charles S., Bufe, Charles G., Frankel, Arthur D., Petersen, Mark D., 2007, Revision of time-Independent probabilistic seismic hazard maps for Alaska: U.S. Geological Survey Open-File Report 2007-1043. [[http://earthquake.usgs.gov/hazards/products/ak/2007/documentation/ofr2007-1043.pdf |Report]]

===== Model Summary Table =====

<wrap info>This table summarises the main characteristics of the original implementation of this model </wrap>

|< 100 5em 60% 40% >|
^ 1          ^ Datasets availability                                                                                                                                                                                                                                                                                                                     ||
| 1.1        | Earthquake catalogue                                                                                                                           | Not available. The catalogue used to develop the model is a combination of several catalogues including the Centennial, PDE, ISC and Alaska Earthquake Information Center                 |
| 1.2        | Geological database                                                                                                                            | Not available. Information comes from different sources (see [[alaska_2007_intro#References|Wesson et al., 2007]] page 12). A good description of major fault is included in the report.  |
| 1.3        | Strong-motion database                                                                                                                         | Not available                                                                                                                                                                             |
| 1.4        | Site characterization database                                                                                                                 | Not available                                                                                                                                                                             |
| //Notes//  |                                                                                                                                                                                                                                                                                                                                           ||
|                                                                                                                                                                                                                                                                                                                                                       |||
^ 2          ^ Methodology for model development                                                                                                                                                                                                                                                                                                         ||
| 2.1        | Scientific participation (SSHAC levels) and review process                                                                                     | Level 2                                                                                                                                                                                   |
| 2.2        | Documentation describing model preparation                                                                                                     | [[alaska_2007_intro#References|Wesson et. al. (2007)]] provides a general description of the methodology adopted for the creation of the hazard model.                                    |
| 2.3        | Codes used for model preparation                                                                                                               | Not available                                                                                                                                                                             |
| //Notes//  |                                                                                                                                                                                                                                                                                                                                           ||
|                                                                                                                                                                                                                                                                                                                                                       |||
^ 3          ^ PSHA input model                                                                                                                                                                                                                                                                                                                          ||
| 3.1        ^ Seismic Source Model                                                                                                                                                                                                                                                                                                                      ||
| 3.1.1      | Area sources                                                                                                                                   | Not included                                                                                                                                                                              |
| 3.1.2      | Grid sources                                                                                                                                   | Gridded seismicity is used to model distributed seismicity in the shallow active crust as well as to model inslab seismicity                                                              |
| 3.1.3      | Crustal faults                                                                                                                                 | Included                                                                                                                                                                                  |
| 3.1.4      | Subduction faults                                                                                                                              | Subduction interface sources modelled as a faults                                                                                                                                         |
| 3.1.5      | Non-parametric ruptures                                                                                                                        | Not included                                                                                                                                                                              |
| 3.1.6      | Magnitude-area scaling relationships                                                                                                           | Not explicitly defined in [[alaska_2007_intro#References|Wesson et. al. (2007)]]                                                                                                          |
| 3.2        ^ Ground Motion Model                                                                                                                                                                                                                                                                                                                       ||
| 3.2.0      | Tectonic regionalisation                                                                                                                       | Sources are classified in accordance with the same tectonic regions used by the USGS to compute hazard for the conterminous United States.                                                |
| 3.2.1      | Models for active shallow seismicity                                                                                                           | Included                                                                                                                                                                                  |
| 3.2.2      | Models for subduction interface                                                                                                                | Included                                                                                                                                                                                  |
| 3.2.3      | Models for subduction intraslab                                                                                                                | Included                                                                                                                                                                                  |
| 3.2.4      | Models for stable continental regions                                                                                                          | Not included                                                                                                                                                                              |
| 3.2.5      | Models for deep non-subduction sources                                                                                                         | Not included                                                                                                                                                                              |
| 3.2.6      | Models for volcanic areas                                                                                                                      | Not included                                                                                                                                                                              |
| 3.3        ^ Site Response Model                                                                                                                                                                                                                                                                                                                       ||
| 3.3.1      | Based on GMPEs                                                                                                                                 | Yes, hazard is computed for a reference soil condition corresponding to NEHRP B/C boundary (Vs30=760 m/s)                                                                                 |
| 3.3.2      | Based on site-response analysis                                                                                                                | No                                                                                                                                                                                        |
| 3.4        ^ Epistemic uncertainties                                                                                                                                                                                                                                                                                                                   ||
| 3.4.1      | Seismic Source Model                                                                                                                           | Not included                                                                                                                                                                              |
| 3.4.2      | Ground Motion Model                                                                                                                            | Included using a logic tree (see  [[alaska_2007_intro#the_ground_Motion_model| the ground motion model]] section)                                                                         |
| 3.4.3      | Site Response Model                                                                                                                            | Not included                                                                                                                                                                              |
| //Notes//  |                                                                                                                                                                                                                                                                                                                                           ||
|                                                                                                                                                                                                                                                                                                                                                       |||
^ 4          ^ Hazard Input Description                                                                                                                                                                                                                                                                                                                  ||
| 4.1        | Hazard input document                                                                                                                          | Not available                                                                                                                                                                             |
| 4.2        | Original input files                                                                                                                           | Available (ASCII input files for the USGS fortran codes)                                                                                                                                  |
| //Notes//  |                                                                                                                                                                                                                                                                                                                                           ||
|                                                                                                                                                                                                                                                                                                                                                       |||
^ 5          ^ Calculation                                                                                                                                                                                                                                                                                                                               ||
| 5.1        | Software                                                                                                                                       | Suite of fortran codes developed by the [[http://earthquake.usgs.gov/hazards/?source=sitenav|USGS]]                                                                                       |
| 5.2        ^ Results                                                                                                                                                                                                                                                                                                                                   ||
| 5.2.1      | Hazard curves                                                                                                                                  | Not directly available                                                                                                                                                                    |
| 5.2.2      | Hazard maps                                                                                                                                    | Not directly available                                                                                                                                                                    |
| 5.2.3      | Uniform hazard spectra                                                                                                                         | Not directly available                                                                                                                                                                    |
| 5.2.4      | Disaggregation                                                                                                                                 | Not directly available                                                                                                                                                                    |
| 5.2.5      | Stochastic event sets                                                                                                                          | Not available                                                                                                                                                                             |
| 5.2.6      | Ground motion fields                                                                                                                           | Not available                                                                                                                                                                             |
| //Notes//  | Almost all the results of a Classical PSHA can be computed with the [[http://earthquake.usgs.gov/hazards/?source=sitenav|USGS]] fortran codes                                                                                                                                                                                             ||


===== Download The OpenQuake-engine Input Model =====

The OpenQuake-engine input model (NRML format) can be downloaded at the link provided below - Please read the license and disclaimer attached to the model. 

<color red/white> N.B. This is a model adapted by GEM Hazard Team to the OpenQuake-engine from the original model developed by the USGS. This explains minor differences you might encounter between the results presented in the OpenQuake platform and those disseminated by the original Organisation.</color>                                                                                                                                                                                                                                         

[[https://platform.openquake.org/documents/91 | Download]]