========
Overview
========

Introduction
------------

Earthquakes remain among the most damaging natural hazards, with more than one million deaths and
nearly a trillion USD in economic losses recorded over the past century. A substantial share of 
these impacts stems from inadequate performance of buildings not designed to satisfy seismic provisions.
This reality makes reliable vulnerability functions essential for producing meaningful loss estimates 
in seismic risk assessments, thereby shaping how risk drivers are identified and how priorities are 
set for mitigation and resilience planning.

This documentation describes the **GEM Global Vulnerability Model**, a comprehensive database of 
fragility and vulnerability functions developed by the Global Earthquake Model (GEM) Foundation 
for seismic risk assessment. The model advances large-scale seismic risk modelling through four 
key pillars:

1. **Expanded building class coverage**: Over 1,000 building classes capturing a wide range of 
   structural systems and seismic design-code levels
   
2. **Improved numerical modelling**: Efficient multi-degree-of-freedom (MDOF) stick-and-mass models 
   to simulate seismic response at scale
   
3. **Extensive ground-motion records**: A comprehensive suite spanning diverse tectonic environments 
   (active shallow crust, stable continental, and subduction zones)
   
4. **New fragility and vulnerability functions**: Tailored specifically to structural damage with 
   explicit treatment of storey-level demands


Building Classification
-----------------------

Buildings are categorised based on primary construction materials, lateral load-resisting systems, 
seismic design code, earthquake-resistant design levels, and height. Each building class is encoded 
using a unique taxonomy string following GEM's taxonomy system.

For instance, ``CR/LFM+CDH+ERH/H:3/RES`` identifies a three-storey (H:3) reinforced concrete (CR) 
moment-resisting frame (LFM) with high code design (CDH), high earthquake-resistant design (ERH), 
and residential (RES) occupancy.

.. list-table:: Building Attributes
   :header-rows: 1
   :widths: 20 15 65

   * - Attribute
     - String
     - Details
   * - **Construction Material**
     - CR
     - Reinforced concrete
   * - 
     - EU
     - Earth construction
   * - 
     - INF
     - Informal construction
   * - 
     - MCF
     - Confined masonry
   * - 
     - MR
     - Reinforced masonry
   * - 
     - MUR
     - Unreinforced masonry
   * - 
     - MUR+ADO
     - Adobe construction
   * - 
     - MUR+CBH
     - Concrete block
   * - 
     - MUR+CLBRH
     - Hollow clay brick
   * - 
     - MUR+CLBRS
     - Solid clay brick
   * - 
     - MUR+STDRE
     - Dressed stone
   * - 
     - MUR+STRUB
     - Rubble stone
   * - 
     - S
     - Steel
   * - 
     - S+MCF
     - Steel and confined masonry
   * - 
     - SRC
     - Concrete composite with steel sections
   * - 
     - W
     - Timber
   * - 
     - W+WBB
     - Bamboo
   * - 
     - W+WWD
     - Wattle and daub
   * - **Lateral Load-Resisting System**
     - LDUAL
     - Dual system
   * - 
     - LFINF
     - Infilled frame
   * - 
     - LFM
     - Moment frame
   * - 
     - LPB
     - Post and beam
   * - 
     - LWAL
     - Wall system
   * - 
     - LFBR
     - Braced frame
   * - **Code Level**
     - CDN
     - Pre-code
   * - 
     - CDL
     - Low code
   * - 
     - CDM
     - Moderate code
   * - 
     - CDH
     - High code
   * - **Earthquake-Resistant Design**
     - ERN
     - No Earthquake-Resistant Design
   * - 
     - ERL
     - Low
   * - 
     - ERM
     - Moderate
   * - 
     - ERH
     - High
   * - 
     - ERS
     - Special
   * - **Height**
     - H:n
     - n is the number of storeys


Methodology Overview
--------------------

The methodology adopted to develop the global vulnerability database consists of:

1. **Numerical Modelling**: Stick-and-mass MDOF systems for over 1,000 building classes
2. **Nonlinear Analysis**: Cloud-based nonlinear time-history analysis (NLTHA) using an extensive 
   suite of ground motions
3. **Fragility Derivation**: Fragility functions characterising structural damage conditional on 
   ground-shaking intensity measures
4. **Vulnerability Assembly**: Comprehensive vulnerability functions combining fragility with 
   damage-to-loss ratios


Data Access
-----------

All derived functions are released in an open-access repository:

* GitHub Repository: https://github.com/gem/global_vulnerability_model


References
----------

* Aljawhari K., Nafeh A.M.B., Silva V. (2025). A New Global Vulnerability Model for Regional 
  Seismic Risk Assessments: Part 1 – Structural Vulnerability.
  
* Martins L., Silva V. (2021). Development of a fragility and vulnerability model for global 
  seismic risk analyses. Bulletin of Earthquake Engineering.
  
* Silva V. et al. (2022). A Building Classification System for Multi-hazard Risk Assessment. 
  International Journal of Disaster Risk Science.