doc edits

docs/pages/Model-Structure.md

@@ -31,6 +31,9 @@ model-directory/
   ├─ model-info.json              (required)
   ├─ calc-config.json             (optional, overrides defaults)
   │
+  ├─ site-data/                   (optional directory of site-specific data)
+  │   └─ ...
+  │
   ├─ active-crust/
   │   ├─ gmm-config.json          (required here or in child source type directory, can override)
   │   ├─ gmm-tree.json
@@ -44,10 +47,10 @@ model-directory/
   │   └─ zone/
   │       └─ ...
   │
-  ├─ stable-crust/...             Same structure as 'active-crust'
+  ├─ stable-crust/                Same structure as 'active-crust'
   │   └─ ...
   │
-  ├─ volcanic/...                 Same structure as 'active-crust'; may include
+  ├─ volcanic/                    Same structure as 'active-crust'; may include
   │   └─ ...                      'decollement' source type
   │
   └─ subduction/
@@ -57,12 +60,16 @@ model-directory/
       ├─ interface/               Similar structure to 'fault' sources
       │   └─ ...
       │
-      └─ slab/                    Similar structure to 'grid' sources
+      ├─ interface-grid/          Similar structure to 'grid' sources
+      │   └─ ...
+      │
+      └─ slab-grid/               Similar structure to 'grid' sources
           └─ ...
 ```
 
 The following sections describe each source type, associated configuration and source definition
-files, and any other requirements.
+files, and any other requirements. The optional `site-data` directory is described
+[at the bottom](#site-data).
 
 ## Crustal Finite Fault Sources
 
@@ -200,6 +207,14 @@ slab/
 
 See also: [Subduction Intraslab Source Type](./Source-Types.md#subduction-intraslab-sources)
 
+## Site Data
+
+TODO  
+
+GMM regions define regions where alternate logic trees of GMMs should be used. Logic trees are
+mapped to tectonic setting and source type. If the source type is `all`, then the value
+[`gmm-tree`](./ModelFiles#gmm-logic-trees) will be used for all source types.
+
 ---
 
 ## Related Pages