Map Sheet 48 (2025 update) - MMI from PGA (2% in 50 years)

The California Geological Survey (CGS) Map Sheet 48 (MS48) provides a depiction of expected ground shaking intensity from future earthquakes across the state. The shaking intensity is represented using the Modified Mercalli Intensity (MMI) scale, which describes the perceived earthquake shaking and correlates strongly with earthquake-induced damage. MS48 maps the level of shaking with a 2% probability of being exceeded in 50 years, equivalent to a 2,475-year average recurrence interval. In addition to MS48, eight interactive MMI hazard maps are presented. These include MMIs calculated using alternative methods. For each method, MMIs at two different hazard levels were presented: one with a 2% probability of being exceeded in 50 years (equivalent to 2,475-year recurrence interval) and the other with 10% probability of being exceeded in 50 years (equivalent to 475-year recurrence interval). The Arc GIS interface allows users to select any two MMI hazard maps to compare side by side. MMI values were calculated using several ground motion to intensity conversion equations (GMICEs). See the “Scientific Background” on MS48 webpage for detailed information. Due to software limitations, symbology cannot be added to this service. To match the symbology used in the MS48 MMI application, use the following configuration: Number of Classes: 7 Classes & Hex Codes: 4 - 5: #ffffbf 5 - 6: #f5f500 6 - 7: #f7ce00 7 - 8: #fa7d00 8 - 9: #fd2a00 9 - 10: #c70808 10 - 11: #8c0808加利福尼亚地质调查局（California Geological Survey, CGS）第48号地图册（MS48）呈现了美国加利福尼亚州未来地震可能引发的地面震动强度分布。该震动强度采用修订麦加利地震烈度（Modified Mercalli Intensity, MMI）量表进行表征，该量表用于描述人们感知到的地震震动情况，且与地震诱发的破坏程度具有强相关性。MS48所映射的震动水平对应50年超越概率为2%的情景，等效于平均重现期2475年。除MS48外，本次还提供了八幅交互式MMI灾害地图，这些地图采用不同计算方法生成。针对每种方法，均展示了两种不同灾害水平下的MMI值：一种为50年超越概率2%（等效重现期2475年），另一种为50年超越概率10%（等效重现期475年）。ArcGIS界面支持用户任选两幅MMI灾害地图进行并排对比。MMI值通过多种地面运动-烈度转换方程（ground motion to intensity conversion equations, GMICEs）计算得到，详细信息可参见MS48网页中的"科学背景"板块。受软件功能限制，本服务无法添加符号系统。若要匹配MS48的MMI应用中所使用的符号系统，请采用如下配置：分级数量：7级；十六进制颜色码：4~5级：#ffffbf；5~6级：#f5f500；6~7级：#f7ce00；7~8级：#fa7d00；8~9级：#fd2a00；9~10级：#c70808；10~11级：#8c0808