User:John.heuver/1985 Algarrobo earthquake

Destruction seen from the earthquake

Article Evaluation

The article is direct in its delivery of information, using informative language to do so. The article lacks deeper information on the geological aspects of the event such as more seismological data on the earthquake. It lists areas affected without specific information on the effects of the earthquake in those areas, which is a distinct flaw in the article. In its defense, the article does include a useful chart on the damage done by the earthquake in terms of people killed, displaced, injured, and also homes destroyed/damaged. The image that this article uses in order to show a map of the event and aftershocks is very bland and not detailed in a way that the reader can understand the full intensity of the earthquake. It is also interesting that it was not possible to find the map that includes the UTC time, ISC event, and magnitude anywhere on the internet as it is shown in the wikipedia article. The article lacks a proper amount of images that show the main kind of damage brought about due to this earthquake. There have been multiple images online in regards to the intensity and the area that the earthquake impacted as can be seen websites such as the USGS but these cannot be used as they are copyrighted and go against wikipedia guidelines. The article however does tell the reader the geographical location, characteristics of the event, and description of the kind of damage suffered during the event. The article however does not talk about what happened including aftershocks and a discussion on the human response to the earthquake or the new scientific understanding that resulted from the event, as well as not including precautions made for future events, if an similar event could take place, and if this event could be used as a model for different locations.

Article Draft

Lead

An earthquake that was registered 7.4 on the Richter scale struck Santiago Chile on March 4, 1985 and ended up killing 177 people and injuring about 2,000 other. This earthquake was not a short felt one nor a minor one as, "The earthquake shook an 800-mile- long stretch of Chile, which hugs South America's southern Pacific coast. People across the Andes Mountains in Argentina, especially in cities in the foothills, also felt the quake"(Press, The Associated). This earthquake was being felt between the northern Antofagasta Region and the southern Araucania Region, meaning that central Chile felt most of the power from the earthquake. This power and damage correlates with its rating on the Mercali intensity scale as the earthquake was felt with a, "Maximum intensity of VIII in the Mercali intensity scale"(Press, The Associated).

Effects

Reports by local residents in the coastal area from Matanzas to several kilometers north of Algarrobo indicate unusually low tides for a period of 3 to 5 days following the earthquake. After this the tides reportedly returned to normal. This suggests that there was earthquake-related uplift along parts of the coast which was recovered in 3 to 5 days after the earthquake. Near Algarrobo, an estimate of the change is about 20 cm uplift.

Tectonic Setting

The earthquake that occurred on March 4, 1985 was not a unique event nor is it an event that will not take place again. The reason behind this is because Chile lies on the boundary between the Nazca plate of the South Pacific continental plate. This means that Chile lies in one of the most seismically active regions in the world, meaning that Chile will continue to face earthquakes that are above 6 on the Richter scale, "It can be seen that on average, a magnitude 8 earthquake or greater (classified as a great event) occurs in the region about once every 25 years"(CA, Taylor. The Institution of Structural Engineers – IStructE). Meaning that there is an expectation that a similar earthquake will happen in Chile in the future every 25 years. The main shock was actually made up of at least two shocks, with the initial motion beginning at approximately 11:00 PM followed by a greater event soon after. The magnitudes of the first and second shocks were calculated to be 5.2 and 6.9 respectively. The calculated proportion of energy released as aftershocks vs the main shock was relatively high, most likely due to the M=7.2 Aftershock on April 9th following the event.

Destroyed road following the earthquake

Scientific Understanding

The 1985 Algarrobo earthquake was seen as a particular powerful earthquake that garnered the attention of the United States, as they sent a team of geologist to study the effects of the earthquake and the overall information that could be gained from studying the earthquake would give better understandings overall of these powerful earthquakes. This earthquake in particular was considered extremely important in the understanding of earthquakes as, "the earthquake was very significant as a geophysical event and that the scientific and engineering study of this major shock would be of great value in improving' our understanding of plate margin earthquakes, the distribution of strong ground motion, resulting building damage and geologic effects such as soil liquefaction and landsliding"(Algermissen, S. T. “USGS.”). The 1985 Algarrobo earthquake shows a clear example of how these types of natural phenomenon can be studied and be used to better help humanity in the future in order to minimize the damages to both infrastructure and human lives. The precautions that Chile takes now in order to mitigate future risks is to educate its citizens in drills on how to react, having better building codes, and studying seismic data, this is stated by seismologist Dr.Sergio Barrientos, "Authorities of Chile have put this problem in the right perspective and have been establishing the right and proper tools to provide more information to citizens and to provide better safety conditions for communities by teaching, and, as I told you, by means of drills"(Welle (www.dw.com)).

Aftershocks

Aftershocks following the May 3, 1985, Chile earthquake (Ms =7.8) yielded an extensive set of digital strong motion recordings. Intense foreshock activity near the epicenter of the main shock occurred for 11 days before the earthquake. The aftershocks of the 1985 earthquake define a rupture area of 170 by 110 square kilometers.

Location & Time

The 1985 Algarrobo earthquake occurred on 3 March at 22:47 UTC (19:47 local time). Its epicenter was located on the south coasts of Valparaíso Region, Chile, close to the beach of Algarrobo.

Damage and effects

Houses affected in San Antonio, Valparaiso, by the 1985 Algarrobo earthquake.

The quake left 177 people dead, 2,575 injured, 85,358 houses damaged or destroyed and about a million people homeless. Many landslides were registered too, pavement breaks with the destruction of Pan-American highway in several points, broken-down bridges and considerable damage in affected town's infrastructure, with a long interruption on basic services. The damage was valued in more than 1 billion US dollars.

Region	Deaths	Injuries	Homeless			Houses
			Refugees	Non-refugees	Total	Destroyed	Minor damage
Valparaíso	68	923	3849	252 800	256 649	17 257	28 242
O'Higgins	28	254	322	190 144	190 466	6661	12 374
Maule	2	60	7	43 411	43 418	2079	5549
Santiago	80	1338	7936	488 075	496 011	59 361	63 814
Total	178	2575	12 114	974 430	986 544	85 358	109 979