Map Sheet 48 (2025 update) - MMI from PGV (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加州地质调查局（California Geological Survey, CGS）第48号图幅（MS48）提供了该州范围内未来地震潜在地面震动烈度的空间分布。该烈度采用修订麦加利烈度（Modified Mercalli Intensity, MMI）尺度进行表征，该尺度用于描述地震感知震动强度，并与地震引发的破坏程度高度相关。MS48所绘制的是50年超越概率为2%的震动烈度水平，等效于2475年的平均重现周期。除MS48外，本数据集还包含八幅交互式MMI烈度灾害图，这些图采用多种替代计算方法生成。针对每种计算方法，数据集提供了两种不同灾害水准下的MMI烈度：其一为50年超越概率2%（等效2475年重现周期），其二为50年超越概率10%（等效475年重现周期）。该服务搭载ArcGIS界面，支持用户任选两幅MMI烈度灾害图进行并排对比。MMI烈度值通过多款地面运动-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（Scientific Background）”板块。受软件限制，本服务无法添加符号系统。若需匹配MS48 MMI应用中所使用的符号系统，请采用如下配置：类别数：7类；十六进制色码：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。