Seismic activity in the context of "Epicenter"

The 1669 eruption of Mount Etna is the largest-recorded historical eruption of that volcano on the east coast of Sicily, Italy. After several weeks of increasing seismic activity that damaged the town of Nicolosi and other settlements, an eruption fissure opened on the southeastern flank of Etna during the night of 10–11 March. Several more fissures became active during 11 March, erupting pyroclastics and tephra that fell over Sicily and accumulated to form the Monti Rossi scoria cone.

Lava disgorged from the eruption fissures and flowed southwards away from the vent, burying farmland and a number of towns during March and April, eventually covering 37–40 square kilometres (14–15 sq mi). The inhabitants of the towns fled to the city of Catania and sought refuge there; religious ceremonies were held in the city to implore the end of the eruption. In early April a branch of the lava flow advanced towards the city, and on the 1 or 16 April it reached the city walls, provoking the flight of many of its inhabitants. The city walls held up the lava, which began to flow into the Ionian Sea. More than two weeks later, parts of the flow surmounted the walls and penetrated Catania but did not cause much damage. The eruption ended in July.

The Valley of Mexico (Spanish: Valle de México; Nahuatl languages: Anahuac, lit. 'Land Between the Waters'), sometimes also called Basin of Mexico, is a highlands plateau in central Mexico. Surrounded by mountains and volcanoes, the Valley of Mexico was a centre for several pre-Columbian civilizations including Teotihuacan, the Toltec, and the Aztec Empire. The valley used to contain five interconnected lakes called Lake Zumpango, Lake Xaltocan (Nahuatl languages: Xāltocān), Lake Xochimilco, Lake Chalco and the largest, Lake Texcoco, covering about 1,500 square kilometers (580 sq mi) of the valley floor. When the Spaniards arrived in the Valley of Mexico, it had one of the highest population concentrations in the world with about one million people. After the conquest of the Aztec Empire, the Spaniards rebuilt the largest and most dominant city, Mēxihco Tenōchtitlan, renaming it Ciudad de México (Mexico City) and over time began to drain the lakes' waters to control flooding.

The Valley of Mexico is located in the Trans-Mexican Volcanic Belt. The valley contains most of the Mexico City metropolitan area, as well as parts of the State of Mexico, Hidalgo, Tlaxcala, and Puebla. The Basin of Mexico covers approximately 9,600 km (3,700 sq mi) in the NNE-SSW direction with length to width dimensions of approximately 125 km (78 miles) to 75 km (47 miles) The Valley of Mexico can be subdivided into four basins, but the largest and most-studied is the area that contains Mexico City. This section of the valley in particular is colloquially referred to as the "Valley of Mexico".The valley has a minimum elevation of 2,200 meters (7,200 ft) above sea level and is surrounded by mountains and volcanoes that reach elevations of over 5,000 meters (16,000 ft). It is an enclosed valley with no natural outlet for water to flow to the sea although there is a gap to the north where there is a high mesa but no high mountain peaks. Within this vulnerable watershed all the native fishes were extinct by the end of the 20th century. Hydrologically, the valley has three features. The first feature is the lakebeds of five now-extinct lakes, which are located in the southernmost and largest of the four sub-basins. The other two features are piedmont, and the mountainsides that collect the precipitation that eventually flows to the lake area. These last two are found in all four of the sub-basins of the valley. Today, the Valley drains through a series of artificial canals to the Tula River, and eventually the Páruco River and the Gulf of Mexico. Seismic activity is frequent here, and the valley is an earthquake-prone zone.

San Miguel (also known as Volcán Chaparrastique) is a stratovolcano in central-eastern El Salvador, approximately 15 kilometres (9.3 mi) southwest of the city of San Miguel. On January 16, 2002, a minor eruption of steam, gas, and ash occurred from the summit crater, lasting 3 hours but causing no real damage to life or property. Carbon dioxide emissions had been monitored since November 2001, and their steady increase continued to build up until the eruption.

Twelve years later, on December 29, 2013, San Miguel erupted at 10:30 local time spewing ash and smoke into the sky, and prompted the evacuation of thousands of people living in a 3 km (1.9 mi) radius around the volcano. It was preceded and caused by increased seismic activity beginning at 06:30 local time.

An aseismic ridge is “a long, linear and mountainous structure that crosses the basin floor of some oceans.” They do not cause earthquakes.

It is called an “aseismic ridge” because they do not receive seismic activity. As a result, they tend to be stable. They are 700-5000 kilometers in length.

Quetzaltenango is a department in the western highlands of Guatemala. The capital is the city of Quetzaltenango, the second largest city in Guatemala. The department is divided up into 24 municipalities. The inhabitants include Spanish-speaking Ladinos and the Kʼicheʼ and Mam Maya groups, both with their own Maya language. The department consists of mountainous terrain, with its principal river being the Samalá River. the department is seismically active, suffering from both earthquakes and volcanic activity.

Prior to the Spanish conquest the territory included in the modern department formed a part of the Kʼicheʼ Kingdom of Qʼumarkaj. The kingdom was defeated by the Spanish under Pedro de Alvarado in a number of decisive battles fought near the city of Quetzaltenango, then known as Xelaju. In the 19th century the territory of the modern department was included in the short-lived Central American state of Los Altos. The department was created by decree in 1845, five years after the fledgling state was crushed by Rafael Carrera.