Ground Shaking (induced earthquake, reservoir fill, dams, cavity collapse, underground explosion, impact, hydrocarbon fields, shale exploration, etc.)

Primary reference(s)

USGS, 2016. EarthWord – Induced Seismicity. United States Geological Survey (USGS). Accessed 21 October 2020.

Additional scientific description

An earthquake is the sudden release of energy and ground shaking resulting from rocks breaking and moving along a fault line. Earthquake ground shaking is produced by seismic waves that travel through the Earth and along its surface. All earthquakes, both natural and man-made, generate seismic waves. Seismic waves radiate outward from the earthquake origin, forming a circular wave front that causes shaking over an extended region (Stein and Wysession, 2003). Ground shaking is a predominant seismic hazard, causing more than 90% of earthquake-related damage and loss (National Institute of Building Sciences Building Seismic Safety Council, 2010).

The strength and duration of the ground shaking at any location depends on many factors, predominantly the magnitude of the earthquake, the earthquake mechanism (i.e., the fault orientation and direction of slip), the distance to the earthquake origin, and local soil conditions (Kramer, 1996; USGS, no date a). Thus, ground shaking at each site from an earthquake is unique and can vary significantly from location to location. There are many human activities that can cause induced earthquakes including: wastewater disposal, mining, development of artificial lakes, extraction of fossil fuels, extraction of groundwater, development of geothermal energy, hydraulic fracturing, and subsurface storage of carbon dioxide.

Earthquake magnitudes are given using one of several broadly equivalent scales, with the ‘moment magnitude’ scaling being the preferred measure of an earthquake’s size, as it quantifies the energy released by the earthquake (USGS, no date b). The magnitude scale is logarithmic; each increase of 1 magnitude unit (i.e., 4.3 to 5.3) represents an order of magnitude (factor of 10) increase in the amplitude of seismic measurements, and a factor of 32 increase in the energy release of an earthquake (USGS, no date b). Earthquakes of Magnitude 7.0 and above can be expected to cause widespread, intense ground shaking; earthquakes of Magnitudes 6.0 to 6.9 may cause local damage. Note that damage may be more severe and widespread for an earthquake of a given magnitude and other characteristics in regions of fragile buildings and high-density population (USGS, no date b).

Metrics and numeric limits

Although there is no globally agreed metric available, there is a global earthquake risk model (Silva et al., 2018) and there are several other Global Earthquake Model Foundation initiatives including a Global Exposure Database for Multi-Hazard Risk Analysis (GEM, no date). The Peak Ground Acceleration method (USGS, no date c; see below for explanation) for measuring ground shaking is the preferred approach, but global use is limited by the distribution of instrumentation.

There are many metrics for measuring ground shaking at a particular location:

• Qualitative intensity measures, like the Modified Mercalli intensity (MMI) scale (Wood and Neumann, 1931), and similar scales such as the Medvedev-Sponheuer-Kárník (MSK) scale or the European Macrointensity Scale (EMS-98) (Grünthal, 1998), describe the severity of an earthquake in terms of its effects on the Earth’s surface, the infrastructure and the population (USGS, no date c). MMI values range from I (not felt) to XII (Total Damage), and the threshold for structural damage begins at VI, although this varies with the fragility of buildings in any given region. For some earthquake reporting agencies, MMI XI and XII are no longer assigned and MMI X is available but has not been applied in recent times. Since 1931, it has become clear that many of the phenomena described by Wood and Neumann (1931) were less related to ground shaking and more to other factors that would promote widespread destruction (Dewey et al., 1995).
• Quantitative measures are direct measures of ground shaking by seismic instruments. A widely used and preferred metric for the strength of ground shaking is Peak Ground Acceleration (PGA). PGA is calculated as the greatest increase in velocity recorded by a particular station during an earthquake (USGS, no date c), and typically given in units of g (the Earth’s gravitational acceleration on its surface; 9.81 m/s2). It is an appropriate measure because the physical force exerted by the ground motions against any object on the surface is proportional to the peak acceleration. For engineering purposes, additional metrics such as spectral acceleration, which measures the forces experienced by structures at specified frequencies to which the structures may be particularly vulnerable. Generally, PGA values of <0.1 g are not expected to cause much damage, while values of between 0.2 g and 0.8 g may cause moderate damage; anything above this is expected to be very damaging (USGS, no date a). It is important to note that the amount of damage caused by ground motions of any given intensity in an area is highly dependent on the strength of infrastructure in that area. The greatest recorded ground motion to date was 4.3 g in the 2008 Iwate-Miyagi earthquake, Japan (Yamada et al., 2010).

Ground shaking can last from a few seconds in small, nearby earthquakes to several minutes in the largest earthquakes. HiQuake is a human induced earthquake database with more than 700 entries across the world for the period 1868 to 2016 (Foulger et al., 2018).

Examples of drivers, outcomes and risk management

On 21 October 2020 the HiQuake database had 1196 recorded events (HiQuake database, no date). These were linked to activities in the following percentages: fracking 33%; mining 25%; water reservoir impoundment 16%; conventional oil and gas 11%; geothermal 6%; waste fluid disposal 4%; nuclear explosion 2%; research 1%; unspecified oil and gas / waste fluid disposal 1%; groundwater extraction 0.6%; deep penetrating bomb 0.3%; construction 0.2%; carbon capture and storage 0.2%; coal bed methane 0.1%; and chemical explosions 0.1%.

Seismic risk from ground shaking is best managed through accurate estimation of the likelihood of seismic ground shaking at damaging levels, the implementation of and conformance to appropriate building codes, and governmental and popular awareness and preparation for earthquakes. Monitoring can be used as a tool to manage anthropogenic activities that cause micro-seismicity, such as rates of fluid or gas discharge into or abstraction from the ground (USGS, no date d).