In reports about past earthquakes, various seismological terms describing earthquake strength are often used, which may cause confusion in the perception of information. It is important to clearly distinguish between two different parameters: seismic intensity (measured in grades and characterizing the impact or effects at a given location) and the size of the earthquake source (evaluated by magnitude or energy class).

Earthquake Intensity (I – intensity) – the seismic effect, assessed in grades according to a descriptive scale of ground shaking intensity. The scale is based on people’s reactions, household object behavior, building and structure performance, as well as changes in landscape and soils. The intensity of a single earthquake varies at different points on the Earth’s surface, depending on the distance from the epicenter. In Kazakhstan, as in the former USSR, the 12-grade seismic scale MSK-64 is used. The maximum value on this scale, as on most similar scales, is 12 grades. It should be emphasized that the intensity of the same earthquake will differ at various points on the surface. The seismic effect observed at a given site depends on the earthquake magnitude, the site’s distance from the epicenter, the depth of the focus, as well as local conditions such as soil quality and groundwater level. In Almaty, during the strongest Verny (1887) and Kemin (1911) earthquakes in history, the intensity reached 9–10 grades.

Other countries use different intensity scales. For example, Japan uses a 7-grade seismic intensity scale (JMA). In the USA and Europe, the 12-grade Modified Mercalli Intensity (MMI) scale is used.

Earthquake Magnitude (M, from Latin magnitudo – size) – a quantitative characteristic of the earthquake source. It is determined from earthquake records (seismograms) at seismic stations. This is a dimensionless value that allows comparison of earthquake sources by their size and energy. The concept of magnitude was first introduced by Charles Richter in 1935 for the classification of earthquakes by source strength. To determine magnitude, the logarithm of the seismogram amplitude was used, normalized to a standard distance. Today, many different magnitude scales exist, differing by method of determination: local magnitude (ML), surface wave magnitude (MS), body wave magnitude (mb, mpv), and moment magnitude (MW). The maximum value on Richter’s original scale was about 9. On the moment magnitude scale (MW), which is physically more accurate for evaluating the strongest earthquakes, magnitudes up to 9.5 are known. Examples include the Chilean earthquake of May 22, 1960 (MW = 9.5) and the Sumatra earthquake of December 26, 2004 (MW = 9.5), which was followed by a devastating tsunami.
Once again, magnitude characterizes the earthquake source. For each event, it is a single value. When people say an earthquake of so-and-so strength “on the Richter scale” was recorded, they are referring to its magnitude. Magnitude is a dimensionless value that helps classify earthquakes by the size of their source.

Types of Structures Without Seismic Reinforcement

• Type A – Adobe brick houses, rural buildings
• Type B – Brick, small-block, large-block buildings
• Type C – Reinforced concrete frame, panel buildings, log houses

Classification of Damage

• Grade 1 (Light): Cracks in plaster
• Grade 2 (Moderate): Small cracks in walls, chimneys
• Grade 3 (Severe): Deep wall cracks, chimney collapse
• Grade 4 (Destruction): Through cracks, collapse of building parts and internal walls
• Grade 5 (Collapse): Total destruction of buildings

Description of Seismic Effects (MSK-64 Intensity Scale)

• 1 grade – Imperceptible. Registered only by instruments.
• 2 grades – Barely perceptible. Felt only by a few people on upper floors.
• 3 grades – Weak. Felt by some people, slight swinging of hanging objects.
• 4 grades – Noticeable shaking. Felt indoors, swinging of hanging objects.
• 5 grades – Awakening. Felt indoors and outdoors, swinging of objects; Grade 1 damage possible in Type A buildings.
• 6 grades – Fright. Furniture falls, people are frightened and run outdoors; Grade 1 damage possible in some Type B and many Type A buildings; isolated landslides.
• 7 grades – Building damage. Fright and panic, many people struggle to stand; Grade 1 damage in many Type C buildings; Grade 2 damage in many Type B buildings; Grade 3 damage in many Type A buildings; landslides and cracks in roads.
• 8 grades – Severe building damage. Grade 2 damage in many Type C buildings; Grade 3 in many Type B; Grade 4 in many Type A; pipeline ruptures; landslides and cracks in roads.
• 9 grades – Widespread building damage. Grade 3 damage in many Type C buildings; Grade 5 damage in many Type A; underground pipeline ruptures; rail track bending.
• 10 grades – General building destruction. Grade 4–5 damage in Type C; Grade 5 damage in Type B; most Type A completely destroyed; dangerous damage to dams, dikes, and underground pipelines; soil cracks 0.2–1.0 m wide; large landslides along riverbanks.
• 11 grades – Catastrophe. Destruction of well-built houses, bridges, dams; railway and highways rendered unusable; mountain rockfalls.
• 12 grades – Change of landscape. Severe damage and destruction of all types of surface and underground structures; radical changes to the Earth’s surface.