Plafker G
Science. 1976 Sep 24;193(4259):1201-8. doi: 10.1126/science.193.4259.1201.
The locations of surface ruptures and the main shock epicenter indicate that the disastrous Guatemala earthquake of 4 February 1976 was tectonic in origin and generated mainly by slip on the Motagua fault, which has an arcuate roughly east-west trend across central Guatemala. Fault breakage was observed for 230 km. Displacement is predominantly horizontal and sinistral with a maximum measured offset of 340 cm and an average of about 100 cm. Secondary fault breaks trending roughly north-northeast to south-southwest have been found in a zone about 20 km long and 8 km wide extending from the western suburbs of Guatemala City to near Mixco, and similar faults with more subtle surface expression probably occur elsewhere in the Guatemalan Highlands. Displacements on the secondary faults are predominantly extensional and dip-slip, with as much as 15 cm vertical offset on a single fracture. The primary fault that broke during the earthquake involved roughly 10 percent of the length of the great transform fault system that defines the boundary between the Caribbean and North American plates. The observed sinistral displacement is striking confirmation of deductions regarding the late Cenozoic relative motion between these two crustal plates that were based largely on indirect geologic and geophysical evidence. The earthquake-related secondary faulting, together with the complex pattern of geologically young normal faults that occur in the Guatemalan Highlands and elsewhere in western Central America, suggest that the eastern wedge-shaped part of the Caribbean plate, roughly between the Motagua fault system and the volcanic arc, is being pulled apart in tension and left behind as the main mass of the plate moves relatively eastward. Because of their proximity to areas of high population density, shallow-focus earthquakes that originate on the Motagua fault system, on the system of predominantly extensional faults within the western part of the Caribbean plate, and in association with volcanism may pose a more serious seismic hazard than the more numerous (but generally more distant) earthquakes that are generated in the eastward-dipping subduction zone beneath Middle America.
地表破裂带的位置及主震震中表明，1976年2月4日危地马拉灾难性地震起源于构造活动，主要由莫塔瓜断层的滑动引发，该断层呈大致东西走向的弧形，横穿危地马拉中部。观测到断层破裂长度达230千米。位移主要为水平方向且向左滑动，最大实测偏移量为340厘米，平均约为100厘米。在从危地马拉城西部郊区延伸至米斯科附近一个长约20千米、宽约8千米的区域内，发现了走向大致为北北东至南南西的次级断层破裂，危地马拉高地其他地方可能也存在地表表现更为细微的类似断层。次级断层上的位移主要为张性和倾滑，单条裂缝的垂直偏移量可达15厘米。地震期间破裂的主断层约占界定加勒比板块与北美板块边界的大型转换断层系统长度的10%。观测到的向左位移有力地证实了关于这两个地壳板块晚新生代相对运动的推断，这些推断主要基于间接的地质和地球物理证据。与地震相关的次级断层活动，以及危地马拉高地和中美洲西部其他地方出现的地质年代较新的复杂正断层模式，表明加勒比板块的东部楔形部分，大致在莫塔瓜断层系统和火山弧之间，正受到张应力作用而被拉开，并在板块主体相对向东移动时被留在后面。由于靠近人口高密度地区，源自莫塔瓜断层系统、加勒比板块西部主要为张性断层系统以及与火山活动相关的浅源地震，可能比在中美洲下方向东倾斜俯冲带产生的更多（但通常距离更远）地震构成更严重的地震危害。
