Earthquakes are bad because they can have a variety of negative impacts, including:
Damage to structures, e.g. Collapse of buildings and walls, breaks in pipes leading to the escape of gas, water and sewage, damage to/failure of bridges, dams etc.
Liquefaction - liquefaction is the process by which water separates from a unconsolidated material such as sand, due to the vibration from an earthquake or other event. Liquefaction can be particularly damaging if it occurs in built-up areas, for example below houses or roads.
Landslides - on steep slopes made unstable due to high levels of rainfall, the vibration from the earthquake may trigger landslides.
Tsunamis - if an earthquake occurs underwater, it can cause displacement of the water above and create a massive wave known as a tsunami.
Demographic impacts - earthquakes can result in large-scale loss of life, evacuation and displacement of people and animals.
Economic impacts - high economic cost due to damage to buildings and infrastructure, loss of revenue due to damage to airports, fishing ports and other industries etc.
Social impacts - homelessness due to building collapse and flooding, mental illnesses such as depression, and bereavement.