2015年尼泊尔地震:廓尔喀地震

The Setting: The Himalayan Collision Zone

Nepal occupies a central position in the Himalayan mountain system, which is formed by the ongoing 板块碰撞两个大陆板块相互汇聚，形成如喜马拉雅山脉般巨大山脉的过程。大陆碰撞带会引发震源浅但威力强大的地震。 of the Indian subcontinent with the Eurasian Plate. The Indian Plate moves northward at approximately 5 centimeters per year and subducts beneath the Tibetan Plateau along the Main Himalayan Thrust — a 汇聚型边界两个板块相互靠近运动的板块边界。可形成俯冲带（海洋—大陆）、造山运动（大陆—大陆），或深海沟（海洋—海洋）。 断层（地质学）岩石沿其发生位移的破裂面。断层长度从数毫米到数千公里不等。会引发地震的主要断层称为活动断层。 system extending over 2,400 kilometers. This collision has been ongoing for approximately 50 million years and has produced the tallest mountain range on Earth. It also generates regular large earthquakes. The historical record documents devastating earthquakes in Nepal in 1255, 1408, 1681, 1833, and 1934. The 1934 Bihar-Nepal earthquake caused widespread damage in the Kathmandu Valley. Seismologists had identified the section of the Main Himalayan Thrust beneath central Nepal as a region of accumulated seismic strain, and a 2013 study by geophysicist Laurent Bollinger and colleagues estimated a high probability of a major earthquake in the coming decades. Nepal's building stock in 2015 was highly vulnerable: the Kathmandu Valley had experienced explosive informal urban growth, and the vast majority of residential buildings were 无筋砌体未配置钢筋加固的砖石或砌块结构，对地震震动极为脆弱。无筋砌体建筑是全球地震死亡人数中占比最高的建筑类型。 brick construction that was known to be highly susceptible to collapse. The 抗震建筑规范为确保建筑物达到最低地震安全水平而制定的一套法律要求，涉及建筑的设计与施工，通常在重大地震暴露出新的薄弱环节后进行修订。 existed on paper but enforcement was nearly nonexistent.

The Earthquake: April 25, 2015

At 11:56 AM local time on April 25, 2015, the Main Himalayan Thrust ruptured approximately 77 kilometers northwest of Kathmandu, near the town of Gorkha. The 震级量化地震所释放总能量的单一数值。震级每增加一个整数单位，释放的能量约增加31.6倍。 was M7.8. The 震源地震破裂在地球内部实际发生的位置，也称焦点。震源深度对地表感受到的震动方式有重大影响。 was approximately 15 kilometers deep, relatively shallow for a continental collision zone. The 断层破裂地震期间岩石沿断层发生破裂，将储存的弹性能量以地震波形式释放的过程。破裂长度小到数米（小地震），大到超过1,000公里（大地震）。 propagated predominantly eastward from the 震中地震发生在地下的震源正上方对应的地表位置，新闻报道中通常将其作为地震发生的位置。, extending roughly 150 kilometers and releasing accumulated strain over a patch of the Main Himalayan Thrust. Kathmandu, a city of approximately 1.5 million people, experienced intense shaking lasting 50 to 60 seconds. The open plazas and central areas of the city — many built on the soft lacustrine sediments of the former Kathmandu lake bed — experienced severe 场地放大效应（土壤放大）软弱土壤或沉积层放大地震波而引起的震动强度增大现象。建在软土上的建筑物所承受的震动强度可达基岩上建筑物的2至10倍。 that increased ground motion by factors of two to four compared to the nearby bedrock sites. Temples, monuments, and 无筋砌体未配置钢筋加固的砖石或砌块结构，对地震震动极为脆弱。无筋砌体建筑是全球地震死亡人数中占比最高的建筑类型。 buildings throughout the historic city center collapsed. At the same time, the earthquake triggered avalanches on the slopes of Mount Everest and surrounding peaks, killing 22 mountaineers at Base Camp in what became the deadliest day in Everest's history.

The Science: A Partially Filled Gap

The 2015 Gorkha earthquake partially filled the seismic gap that geophysicists had identified beneath central Nepal, but it did not fill the entire locked patch. 干涉合成孔径雷达（InSAR）通过对比地震前后拍摄的雷达图像，以厘米级精度测量地表形变的卫星雷达技术，可揭示断层的滑动模式。 satellite data and GPS大地测量利用全球定位系统接收机以毫米级精度测量构造板块运动和地壳变形的方法，可揭示地震之间断层上应变积累的过程。 measurements showed that the earthquake ruptured the deeper, updip portion of the locked fault zone but did not propagate all the way to the surface — a pattern described as a blind thrust rupture. The remaining locked portions of the Main Himalayan Thrust still carry significant accumulated strain, meaning the 2015 earthquake did not fully relieve the seismic potential of the region. This finding had important implications for 余震在同一断层区域内、发生于主震之后的较小地震。余震序列可持续数周至数年，最大余震的震级通常比主震低1.0至1.2级。 assessment: not only was the existing ruptured zone subject to stress re-adjustment 余震在同一断层区域内、发生于主震之后的较小地震。余震序列可持续数周至数年，最大余震的震级通常比主震低1.0至1.2级。 sequences, but the adjacent unruptured segments may have had their failure probability increased by 库仑应力传递地震改变邻近断层应力状态、从而可能触发或延迟未来地震的过程，用于预测哪些断层正被推向更接近破裂的状态。 transfer from the mainshock. The largest 余震在同一断层区域内、发生于主震之后的较小地震。余震序列可持续数周至数年，最大余震的震级通常比主震低1.0至1.2级。, a M7.3 on May 12, 2015, struck east of the main rupture zone, in exactly the area where stress transfer models predicted elevated failure probability. Use the Earthquake Energy Calculator to understand how the M7.3 aftershock relates energetically to the M7.8 mainshock.

The Impact: Kathmandu and Mountain Communities

The 2015 Nepal earthquake killed 8,964 people and injured over 22,000. Approximately 604,000 houses were destroyed and another 288,000 were damaged. The Kathmandu Valley, despite being the center of population and government, was not the hardest-hit area relative to its size. The most severe devastation occurred in the hill districts northwest of Kathmandu — Gorkha, Sindhupalchowk, and Rasuwa — where remote mountain villages built of traditional stone 无筋砌体未配置钢筋加固的砖石或砌块结构，对地震震动极为脆弱。无筋砌体建筑是全球地震死亡人数中占比最高的建筑类型。 were almost entirely obliterated. Road access to these districts was poor even before the earthquake, and landslides triggered by the shaking blocked mountain roads for days. The mountainous terrain made helicopter evacuation the only option for many communities. The historic structures of Kathmandu — temples, stupas, and palace complexes in the Durbar Squares of Kathmandu, Patan, and Bhaktapur — suffered severe damage, with UNESCO World Heritage sites destroyed or partially collapsed. The 搜救（SAR）地震后有组织地开展定位并救出被困于倒塌建筑物中幸存者的行动。震后头72小时是发现生还者的关键窗口期。 operations were complicated by the scale of affected area: roughly 500,000 square kilometers of territory across Nepal, India, China, and Bangladesh experienced moderate to strong shaking.

The Response: International Aid and Local Challenges

The international 搜救（SAR）地震后有组织地开展定位并救出被困于倒塌建筑物中幸存者的行动。震后头72小时是发现生还者的关键窗口期。 response to the 2015 Nepal earthquake was the largest ever deployed in the Himalayan region. Over 60 countries offered assistance. Urban search and rescue teams from China, India, Israel, Japan, the UK, and the United States arrived within 48 hours. The Nepali Army and Armed Police Force were mobilized in full. However, several structural challenges hampered the response. Nepal's single international airport in Kathmandu became severely congested as aid flights arrived simultaneously. The road network in the hill districts was inadequate for the scale of aid movement required. Government coordination structures were strained. The combination of 抗震建筑规范为确保建筑物达到最低地震安全水平而制定的一套法律要求，涉及建筑的设计与施工，通常在重大地震暴露出新的薄弱环节后进行修订。 enforcement failure, geographic remoteness, and infrastructure inadequacy created a response environment in which the gap between arriving international aid and reaching the most severely affected communities could be measured in days to weeks rather than hours.

The Legacy: Building Back Better

The 2015 Nepal earthquake generated enormous international attention and billions of dollars in reconstruction pledges. The National Reconstruction Authority was established to oversee rebuilding. Nepal's building codes were reviewed and strengthened. A major debate emerged about whether to rebuild traditional stone architecture — culturally irreplaceable but seismically vulnerable — or to shift entirely to reinforced concrete construction more resistant to 余震在同一断层区域内、发生于主震之后的较小地震。余震序列可持续数周至数年，最大余震的震级通常比主震低1.0至1.2级。 sequences. The resolution was a hybrid approach: culturally significant structures rebuilt using traditional techniques with hidden reinforcement, while ordinary residential buildings encouraged to adopt confined masonry or reinforced concrete frames. Critically, the 余震在同一断层区域内、发生于主震之后的较小地震。余震序列可持续数周至数年，最大余震的震级通常比主震低1.0至1.2级。 sequence — including the M7.3 May 12 event — demonstrated that 抗震建筑规范为确保建筑物达到最低地震安全水平而制定的一套法律要求，涉及建筑的设计与施工，通常在重大地震暴露出新的薄弱环节后进行修订。 compliance during reconstruction was not just aspirational but immediately life-saving, as the few new buildings that met seismic standards performed dramatically better than the legacy stock in the aftershock-damaged hillside communities.