The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise loc...The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise locations of earthquakes since 1968, geodetic data and fault offsets for the 1906 great shock are used to re-examine the timing and locations of possible future large earthquakes. The physical mechanisms of regional faults like the Calaveras, Hayward and Sargent, which exhibit creep, differ from those of the northern San Andreas, which is currently locked and is not creeping. Much decadal forerunning activity occurred on creeping faults. Moderate-size earthquakes along those faults became more frequent as stresses in the region increased in the latter part of the cycle of stress restoration for major and great earthquakes along the San Andreas. They may be useful for decadal forecasts. Yearly to decadal forecasts, however, are based on only a few major to great events. Activity along closer faults like that in the two years prior to the 1989 Loma Prieta shock needs to be examined for possible yearly forerunning changes to large plate boundary earthquakes. Geodetic observations are needed to focus on identifying creeping faults close to the San Andreas. The distribution of moderate-size earthquakes increased significantly since 1990 along the Hayward fault but not adjacent to the San Andreas fault to the south of San Francisco compared to what took place in the decades prior to the three major historic earthquakes in the region. It is now clear from a re-examination of the 1989 mainshock that the increased level of moderate-size shocks in the one to two preceding decades occurred on nearby East Bay faults. Double-difference locations of small earthquakes provide structural information about faults in the region, especially their depths. The northern San Andreas fault is divided into several strongly coupled segments based on differences in seismicity.展开更多
文摘The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise locations of earthquakes since 1968, geodetic data and fault offsets for the 1906 great shock are used to re-examine the timing and locations of possible future large earthquakes. The physical mechanisms of regional faults like the Calaveras, Hayward and Sargent, which exhibit creep, differ from those of the northern San Andreas, which is currently locked and is not creeping. Much decadal forerunning activity occurred on creeping faults. Moderate-size earthquakes along those faults became more frequent as stresses in the region increased in the latter part of the cycle of stress restoration for major and great earthquakes along the San Andreas. They may be useful for decadal forecasts. Yearly to decadal forecasts, however, are based on only a few major to great events. Activity along closer faults like that in the two years prior to the 1989 Loma Prieta shock needs to be examined for possible yearly forerunning changes to large plate boundary earthquakes. Geodetic observations are needed to focus on identifying creeping faults close to the San Andreas. The distribution of moderate-size earthquakes increased significantly since 1990 along the Hayward fault but not adjacent to the San Andreas fault to the south of San Francisco compared to what took place in the decades prior to the three major historic earthquakes in the region. It is now clear from a re-examination of the 1989 mainshock that the increased level of moderate-size shocks in the one to two preceding decades occurred on nearby East Bay faults. Double-difference locations of small earthquakes provide structural information about faults in the region, especially their depths. The northern San Andreas fault is divided into several strongly coupled segments based on differences in seismicity.
文摘【目的】探究‘海沃德’‘华特’猕猴桃果实采后影响抗坏血酸(ascorbic acid,AsA)氧化的相关酶活性及基因表达差异,为猕猴桃采后AsA氧化机制的系统研究,调控果实成熟和衰老进程,并有效保持果实采后品质和延长贮藏时间等研究提供理论依据。【方法】以‘海沃德’‘华特’猕猴桃作为试验材料,测定两个品种的果实在采后25℃贮藏条件下AsA、总抗坏血酸(total ascorbic acid,T-AsA)、脱氢抗坏血酸(dehydroascorbic acid,DHA)、AsA/DHA、与AsA氧化相关的抗坏血酸氧化酶(ascorbic acd oxidase,AO)、漆酶(Laccase)、抗坏血酸过氧化物酶(ascorbate peroxidase,APX)的活性及相关酶基因的表达,研究两个品种猕猴桃果实AsA含量变化与AO、漆酶、APX活性及相关酶基因的相关性。【结果】‘海沃德’猕猴桃采后初期AsA含量为86.9 mg/100 g FW,到贮藏末期损失约45%,而‘华特’猕猴桃在采后初期AsA含量较高,为610 mg/100 g FW,中期上升至峰值886 mg/100 g FW,末期下降到778 mg/100 g FW,高于采后第1天AsA含量,整体呈上升趋势;两个品种DHA含量在整个贮藏期整体呈下降趋势,但‘海沃德’猕猴桃中DHA含量始终低于‘华特’;T-AsA含量与其AsA含量的变化趋势接近;整个贮藏后期,‘海沃德’猕猴桃的AsA/DHA比值远低于‘华特’。AO活性与两个品种猕猴桃AsA含量呈显著负相关性,漆酶活性与两个品种猕猴桃AsA含量呈负相关性;从采后第8天开始,‘华特’的AO活性低于‘海沃德’,在整个贮藏期,‘华特’猕猴桃中漆酶活性都低于‘海沃德’;且在采后第11天,‘华特’中AO和漆酶活性均达到最低值,‘海沃德’中漆酶活性在采后第16天达到最高值;APX对AsA含量的影响较小,其活性与AsA变化无显著相关性。AO基因家族中的3个基因中,Achn020161是AsA氧化分解的关键基因,而Achn191341和Achn316521与AsA的氧化无显著相关性;漆酶基因家族中的3个基因中,Achn007661、Achn191341对AsA含量变化有一定影响,而Achn163871与AsA的氧化无显著相关性;APX基因家族中的Achn123021、Achn082241、Achn187071对AsA含量的变化有一定影响,但均不是氧化AsA的关键基因。【结论】AsA/DHA的高比值对AsA的积累起重要作用,AO是氧化AsA的关键酶,漆酶对AsA氧化有一定作用,APX不是主要氧化AsA的酶,推测AO基因家族中的Achn020161是氧化AsA的关键基因,而漆酶基因家族中的Achn007661与Achn19134对氧化AsA有一定作用。
