【正文】 ude or greater and 20 have been greater than . The aftershock zone stretches across 25 miles from just north of Los Gatos near Highway 17, to south of Watsonville near Highway 101. This zone corresponds with the areas of greatest damage. The zone ranges from about 2 to 11 miles in depth and is believed to be the length of rupture associated with the main shock. Surface Effects Surface displacements with offsets of up to 3 or 4 feet along a zone about 20 miles long would normally be expected to acpany an earthquake of this magnitude. Instead many cracks have been found over several discontinuous and indistinct zones. There are several possible explanations for this lack of clear surface expression. The earthquake was unusually deep, making it difficult for the bedrock rupture to propagate to the ground surface. The bination of rugged topography, thick soil, and forest cover could also make surface breaks less distinct. The State Commission report of the 1906 earthquake described very similar surface rupture characteristics along the Santa Cruz Mountains portion of the San Andreas Fault. Historical Seismicity The San Andreas Fault trends northwesterly and extends more than 800 miles from the Gulf of California to Cape Mendocino north of San Francisco. It has been the source of many large earthquakes including an 1838 earthquake located on the peninsula south of San Francisco (magnitude in excess of ), an 1865 earthquake northeast of Santa Cruz, and the famous 1906 San Francisco Earthquake with magnitude . The Loma Prieta Earthquake essentially repeats the 1865 event and is the first major rupture along the San Andreas since 1906. The length of fault rupture generally extended from the southern end of the 1906 break and thus relieved strain, which had accumulated since before that time. The lack of activity on this section of the fa ult, as well as the occurrence of several magnitude + events in the area over the last two years, had prompted geologists to forecast this event The most recent damaging earthquakes in the Santa Cruz area include a magnitude earthquake on November 15, 1964, which resulted in broken chimneys。 外文翻譯 指導(dǎo)教師： 趙同峰 專業(yè)班級(jí)：土木 07— 3 班 學(xué) 號(hào)： 0702090306 姓 名： 王巍 沈陽(yáng)建筑大學(xué) 土木工程學(xué)院 英文資料 The October 17, 1989 Loma Prieta Earthquake October 1989 Commercial Structures The Loma Prieta Earthquake and its subsequent aftershocks resulted in widespread damage to a variety of mercial structures. A large geographical area was affected, as is typical for an earthquake of this magnitude. The affected area enpasses eight counties, from Monterey and San Benito in the south to San Francisco, Alameda, and Contra Costa in the north. In total, building structures experienced damage over an area of approximately 3,000 square miles. Although damage was widespread, it was also quite sporadic. As would be expected, areas closest to the epicenter including Hollister, Los Gatos, Santa Cruz, and Watsonville experienced the most concentrated damage. Farther away, heavy damage was generally limited to buildings of very poor construction founded on soft soils that failed or amplified the earthquake ground motions. This is similar to the effects noted in the 1985 Mexico City Earthquake. Earthquake effects also tended to be highly directional. Most damage occurred within a narrow band that extends northwest to southeast, approximately paralleling the San Andreas Fault. Thus many munities along the margins of San Francisco Bay escaped serious damage. Unreinforced Masonry Buildings As has been observed in past California earthquakes, the most concentrated and severe damage to building structures occurred in unreinforced masonry (URM) bearingwall buildings. URM buildings, constructed of woodframe roof and floor systems supported by thick unreinforced brick walls, were monly constructed throughout California until the 1930s, when the adoption of building codes with seismicresistive provisions prevented their further development. As a result, URM buildings are typically found in the central business districts of older California cities Failures of URM buildings result from inadequate anchorage of the masonry walls to roof and floor diaphragms, as well as the limited strength and ductility of the basic building materials and poor construction workmanship. Deterioration of the sandlime mortar and wood framing due to weather exposure frequently contributes to poor performance. California has recently enacted legislation (SB 547) requiring cities to identify URM buildings and develop plans to reduce the risk they present. Damage to URM buildings in the Loma Prieta Earthquake ranged from dramatic collapses near the epicenter to fallen parapets in Martinez, more than 70 miles away. Lifethreatening collapses also occurred in Hollister, Los Gatos, Oakland, and the San Francisco financial district. The roofs and floors in many buildings with collapsed walls seemingly defied gravity by continuing to stand after losing their loadbearing support. Generally, buildings with throughwall anchorage to floor and roof framing performed better than buildings without this feature. Most URM buildings in the region survived the earthquake without collapse or obvious substantial damage. However, field investigations show that many of these structures have experienced extensive cracking of the masonry and are therefore weakened. If not repaired, some of these buildings are likely to collapse in future earthquakes. URM buildings with more than three or four stories were generally constructed with steel frames to carry the gravity loads. Masonry walls in these buildings were primarily provided for building closu