Merge branch 'docs-impl-details-start' into 'main'

Implementation details doc page

See merge request !587

docs/README.md

@@ -6,7 +6,7 @@ National Seismic Hazard Model Project ([NSHMP](https://earthquake.usgs.gov/hazar
 USGS's earthquake hazards program ([EHP](http://earthquake.usgs.gov)).
 
 *nshmp-haz* supports high performance seismic hazard calculations required to generate detailed
-maps over large areas and supports a variety of USGS web services and applications related to
+maps over large areas and supports a variety of web services and applications related to
 seismic hazards research and the dissemination of hazard data (see the
 [NSHM Hazard Tool](https://earthquake.usgs.gov/nshmp/)). This documentation explains how to
 use *nshmp-haz* as well as underlying model implementation details.
@@ -27,6 +27,7 @@ use *nshmp-haz* as well as underlying model implementation details.
   * [Magnitude Frequency Distributions (MFDs)](./pages/Magnitude-Frequency-Distributions.md)
   * [Rupture Scaling Relations](./pages/Rupture-Scaling-Relations.md)
   * [Ground Motion Models (GMMs)](./pages/Ground-Motion-Models.md)
+* [Implementation Details](./pages/Implementation-Details.md)
 * [USGS Models](./pages/USGS-Models.md)
   * [Model Editions](./pages/Model-Editions.md)
   * [Logic Trees & Uncertainty](./pages/Logic-Trees-&-Uncertainty.md)

docs/pages/Implementation-Details.md

+# Implementation Details
+
+## Logic Trees
+
+The logic trees of epistemic uncertainty described in previous section are represented internally
+using graphs of indexed nodes that connect a `root` node with one or more `leaf` nodes:
+
+![image](images/tree-example.png "Example logic tree graph")
+
+The different logic trees for sources, MFDs and GMMs have similar representations:
+
+![image](images/tree-types.png "Primary logic tree types")
+
+And each unique branch combination across all trees is considered in the hazard integral:
+
+![image](images/tree-branches-combined.png "Logic tree branch combination")
+
+---
+
+[**Documentation Index**](../README.md)
+
+---
+![USGS logo](./images/usgs-icon.png)  [U.S. Geological Survey](https://www.usgs.gov)
+National Seismic Hazard Mapping Project ([NSHMP](https://earthquake.usgs.gov/hazards/))